# Finding a Non Transitive Coprime Triplet in a Range

Given L and R, find a possible non transitive triplet (a, b, c) such that pair (a, b) is coprime and pair (b, c) is coprime but (a, c) is not coprime.
Eg: (2, 5, 6) is a non transitive triplet as pair (2, 5) is coprime and pair (5, 6) is coprime but pair (2, 6) is not coprime

Examples:

Input : L = 2, R = 10
Output : a = 4, b = 7, c = 8 is one such triplet
Explanation (4, 7, 8) is a possible triplet (while there are also other such triplets present in this range), Here, pair (4, 7) is coprime and pair (7, 8) is coprime but the pair (4, 8) is not coprime

Input : L = 21, R = 47
Output : a = 23, b = 25, c = 46 is one such triplet
Explanation (23, 25, 46) is a possible triplet (while there are also other such triplets present in this range), Here, pair (23, 25) is coprime and pair (25, 46) is coprime but the pair (23, 46) is not coprime

Method 1 ( Brute Force) :

We generate all possible Triplets between L and R and check if the property holds true that pair (a, b) is coprime and pair (b, c) is coprime but pair (a, c) isn’t.

## C++

 // C++ program to find possible non transitive triplets btw L and R #include using namespace std;    // Function to return gcd of a and b int gcd(int a, int b) {     if (a == 0)         return b;     return gcd(b % a, a); }    // function to check for gcd bool coprime(int a, int b) {     // a and b are coprime if their gcd is 1.     return (gcd(a, b) == 1); }    /* Checks if any possible triplet (a, b, c) satisfying the condition    that (a, b) is coprime, (b, c) is coprime but (a, c) isnt */ void possibleTripletInRange(int L, int R) {        bool flag = false;     int possibleA, possibleB, possibleC;        // Generate and check for all possible triplets     // between L and R     for (int a = L; a <= R; a++) {         for (int b = a + 1; b <= R; b++) {             for (int c = b + 1; c <= R; c++) {                    // if we find any such triplets set flag to true                 if (coprime(a, b) && coprime(b, c) && !coprime(a, c)) {                     flag = true;                     possibleA = a;                     possibleB = b;                     possibleC = c;                     break;                 }             }         }     }        // flag = True indicates that a pair exists     // between L and R     if (flag == true) {         cout << "(" << possibleA << ", " << possibleB              << ", " << possibleC << ")"              << " is one such possible triplet between "              << L << " and " << R << "\n";     }     else {         cout << "No Such Triplet exists between "              << L << " and " << R << "\n";     } }    // Driver code int main() {     int L, R;        // finding possible Triplet between 2 and 10     L = 2;     R = 10;     possibleTripletInRange(L, R);        // finding possible Triplet between 23 and 46     L = 23;     R = 46;     possibleTripletInRange(L, R);        return 0; }

## Java

 // Java program to find possible non  // transitive triplets btw L and R class GFG {            // Function to return gcd of a and b     static int gcd(int a, int b)     {         if (a == 0)             return b;                        return gcd(b % a, a);     }        // function to check for gcd     static boolean coprime(int a, int b)     {                    // a and b are coprime if their          // gcd is 1.         return (gcd(a, b) == 1);     }        // Checks if any possible triplet      // (a, b, c) satifying the condition     // that (a, b) is coprime, (b, c) is     // coprime but (a, c) isnt */     static void possibleTripletInRange(int L, int R)     {            boolean flag = false;         int possibleA = 0, possibleB = 0,                             possibleC = 0;            // Generate and check for all possible         // triplets between L and R         for (int a = L; a <= R; a++) {             for (int b = a + 1; b <= R; b++) {                 for (int c = b + 1; c <= R; c++)                 {                        // if we find any such triplets                     // set flag to true                     if (coprime(a, b) && coprime(b, c)                                     && !coprime(a, c))                     {                         flag = true;                         possibleA = a;                         possibleB = b;                         possibleC = c;                         break;                     }                 }             }         }            // flag = True indicates that a pair exists         // between L and R         if (flag == true) {             System.out.println("(" + possibleA + ", "                    + possibleB + ", " + possibleC + ")"                     + " is one such possible triplet "                       + "between " + L + " and " + R);         }         else {             System.out.println("No Such Triplet exists"                       + "between " + L + " and " + R);         }     }        // Driver code     public static void main(String[] args)     {                    int L, R;            // finding possible Triplet between         // 2 and 10         L = 2;         R = 10;         possibleTripletInRange(L, R);            // finding possible Triplet between          // 23 and 46         L = 23;         R = 46;         possibleTripletInRange(L, R);     } }    // This code is contributed by // Smitha DInesh Semwal

## Python3

 # Python3 program to find possible non  # transitive triplets btw L and R    # Function to return gcd of a and b def gcd(a, b):        if (a == 0):         return b;     return gcd(b % a, a);    # function to check for gcd def coprime(a, b):        # a and b are coprime if     # their gcd is 1.     return (gcd(a, b) == 1);    # Checks if any possible triplet  # (a, b, c) satifying the condition # that (a, b) is coprime, (b, c)  # is coprime but (a, c) isnt  def possibleTripletInRange(L, R):        flag = False;     possibleA = 0;     possibleB = 0;     possibleC = 0;        # Generate and check for all      # possible triplets between L and R     for a in range(L, R + 1):          for b in range(a + 1, R + 1):              for c in range(b + 1, R + 1):                                    # if we find any such triplets                  # set flag to true                 if (coprime(a, b) and coprime(b, c) and                                            coprime(a, c) == False):                     flag = True;                     possibleA = a;                     possibleB = b;                     possibleC = c;                     break;        # flag = True indicates that a      # pair exists between L and R     if (flag == True):          print("(", possibleA, ",", possibleB,                ",", possibleC, ") is one such",                "possible triplet between", L, "and", R);     else:         print("No Such Triplet exists between",                                   L, "and", R);    # Driver Code    # finding possible Triplet # between 2 and 10 L = 2; R = 10; possibleTripletInRange(L, R);    # finding possible Triplet  # between 23 and 46 L = 23; R = 46; possibleTripletInRange(L, R);    # This code is contributed by mits

## C#

 // C# program to find possible  // non transitive triplets  // btw L and R using System; class GFG  {     // Function to return     // gcd of a and b     static int gcd(int a,                    int b)     {         if (a == 0)             return b;                        return gcd(b % a, a);     }        // function to     // check for gcd     static bool coprime(int a,                          int b)     {                    // a and b are coprime          // if their gcd is 1.         return (gcd(a, b) == 1);     }        // Checks if any possible      // triplet (a, b, c) satifying      // the condition that (a, b)      // is coprime, (b, c) is     // coprime but (a, c) isnt */     static void possibleTripletInRange(int L,                                         int R)     {            bool flag = false;         int possibleA = 0,              possibleB = 0,              possibleC = 0;            // Generate and check for         // all possible triplets          // between L and R         for (int a = L; a <= R; a++)          {             for (int b = a + 1;                       b <= R; b++)             {                 for (int c = b + 1;                           c <= R; c++)                 {                        // if we find any                      // such triplets                     // set flag to true                     if (coprime(a, b) &&                          coprime(b, c) &&                         !coprime(a, c))                     {                         flag = true;                         possibleA = a;                         possibleB = b;                         possibleC = c;                         break;                     }                 }             }         }            // flag = True indicates          // that a pair exists         // between L and R         if (flag == true)         {             Console.WriteLine("(" + possibleA + ", " +                                      possibleB + ", " +                                      possibleC + ")" +                      " is one such possible triplet " +                          "between " + L + " and " + R);         }         else          {             Console.WriteLine("No Such Triplet exists" +                           "between " + L + " and " + R);         }     }        // Driver code     public static void Main()     {         int L, R;            // finding possible          // Triplet between         // 2 and 10         L = 2;         R = 10;         possibleTripletInRange(L, R);            // finding possible          // Triplet between          // 23 and 46         L = 23;         R = 46;         possibleTripletInRange(L, R);     } }    // This code is contributed // by anuj_67.

## PHP



Output:

(8, 9, 10) is one such possible triplet between 2 and 10
(44, 45, 46) is one such possible triplet between 23 and 46

Time Complexity of the Brute Force Solution is O(n3log(A)) where A is the smallest number of the triplet.
Note: The log factor of the complexity is that of computing the GCD for a pair of numbers.

Method 2 (efficient):

Since we need only one such possible pair, we can use this to breakdown our complexity further.

We just need to identify some cases and look to solve those to solve this problem.

Case 1: There are less than 3 numbers between L and R.
This Case is easy, we cant form any triplets so the answer is this case would always be ‘Not Possible’

Case 2: There are more than three numbers between L and R.
Now,
Its a well known proof that consecutive numbers are always coprime. We can even prove this easily.

Proof:
Given that N and N + 1 are two consecutive integers.
Now suppose gcd(n, n + 1) = X,
? X divides n and X also divides (n + 1).
Which implies that X divides ((n + 1) - n) or X divides 1.
But, There is no number which divides 1 except 1.
? X = 1, or we can also say that gcd(n, n + 1) = 1

Thus, n and n + 1 are coprime.

So, if we take three consecutive numbers of the form 2k, 2k + 1, 2k + 2 we would always end up having a possible triplet because as proved above, pairs (2k, 2k + 1) and (2k + 1, 2k + 2) being pairs of consecutive numbers are coprime and the pair (2k, 2k+2) have their gcd as 2 (since they are even).

Case 3: When there are exactly 3 numbers between L and R
This is extension of case 3, now this case can have 2 cases,

Case 3.1 When the three numbers are of the form 2k, 2k + 1, 2k + 2
We have already looked at this case in case 2. So this is the only triplet and also is a valid triplet between L and R.

Case 3.2 When the three numbers are of the form 2k – 1, 2k, 2k + 1
We have already seen that (2k – 1, 2k) and (2k, 2k + 1) being pair of consecutive numbers are coprime pairs so we need to check if the pair (2k – 1, 2k + 1) is coprime or not
It can be proved that the pair (2k – 1, 2k + 1) is always coprime as shown below

Proof:
Given that 2k - 1 and 2k + 1 are two numbers
Now suppose gcd((2k - 1), (2k + 1)) = X,
? X divides (2k - 1) and X also divides (2k + 1).
Which implies that X divides ((2k + 1) - (2k - 1)) or X divides 2.
2 being a prime is only divisible by 1 and 2 itself.
But, 2k - 1 and 2k + 1 are odd numbers so X can never be equal to 2.
? X = 1, or we can also say that gcd((2k -1), (2k + 1)) = 1

Thus, 2k - 1 and 2k + 1 are coprime.

Thus, in this case we wont be able to find any possible valid triplet.

Below is the implementation of above approach:

## C++

 /* C++ program to find a non transitive co-prime    triplets between L and R */ #include using namespace std;    /* Checks if any possible triplet (a, b, c) satisfying the condition    that (a, b) is coprime, (b, c) is coprime but (a, c) isnt */    void possibleTripletInRange(int L, int R) {        bool flag = false;     int possibleA, possibleB, possibleC;        int numbersInRange = (R - L + 1);        /* Case 1 : Less than 3 numbers between L and R */     if (numbersInRange < 3) {         flag = false;     }        /* Case 2: More than 3 numbers between L and R */     else if (numbersInRange > 3) {         flag = true;            // triplets should always be of form (2k, 2k + 1, 2k + 2)         if (L % 2) {             L++;         }            possibleA = L;         possibleB = L + 1;         possibleC = L + 2;     }        else {         /* Case 3.1: Exactly 3 numbers in range of form                      (2k, 2k + 1, 2k + 2) */         if (!(L % 2)) {             flag = true;             possibleA = L;             possibleB = L + 1;             possibleC = L + 2;         }         else {             /* Case 3.2: Exactly 3 numbers in range of form                          (2k - 1, 2k, 2k + 1) */             flag = false;         }     }        // flag = True indicates that a pair exists between L and R     if (flag == true) {         cout << "(" << possibleA << ", " << possibleB              << ", " << possibleC << ")"              << " is one such possible triplet between "              << L << " and " << R << "\n";     }     else {         cout << "No Such Triplet exists between "              << L << " and " << R << "\n";     } }    // Driver code int main() {     int L, R;        // finding possible Triplet between 2 and 10     L = 2;     R = 10;     possibleTripletInRange(L, R);        // finding possible Triplet between 23 and 46     L = 23;     R = 46;     possibleTripletInRange(L, R);        return 0; }

## Java

 // Java program to find a  // non transitive co-prime // triplets between L and R  import java.io.*;    class GFG  {    // Checks if any possible triplet  // (a, b, c) satifying the condition // that (a, b) is coprime, (b, c)  // is coprime but (a, c) isnt static void possibleTripletInRange(int L,                                     int R) {     boolean flag = false;     int possibleA = 0,          possibleB = 0,          possibleC = 0;         int numbersInRange = (R - L + 1);        // Case 1 : Less than 3      // numbers between L and R     if (numbersInRange < 3)      {         flag = false;     }        // Case 2: More than 3      // numbers between L and R      else if (numbersInRange > 3)     {         flag = true;            // triplets should always          // be of form (2k, 2k + 1,         // 2k + 2)         if (L % 2 > 0)          {             L++;         }            possibleA = L;         possibleB = L + 1;         possibleC = L + 2;     }        else      {         /* Case 3.1: Exactly 3 numbers                        in range of form                      (2k, 2k + 1, 2k + 2) */         if (!(L % 2 > 0))          {             flag = true;             possibleA = L;             possibleB = L + 1;             possibleC = L + 2;         }         else          {             /* Case 3.2: Exactly 3 numbers                          in range of form                          (2k - 1, 2k, 2k + 1) */             flag = false;         }     }        // flag = True indicates      // that a pair exists      // between L and R     if (flag == true)      {         System.out.println("(" + possibleA +                           ", " + possibleB +                            ", " + possibleC +               ")" + " is one such possible" +                         " triplet between " +                            L + " and " + R );     }     else {         System.out.println("No Such Triplet" +                            " exists between " +                               L + " and " + R);     } }    // Driver code public static void main (String[] args)  { int L, R;    // finding possible Triplet  // between 2 and 10 L = 2; R = 10; possibleTripletInRange(L, R);    // finding possible Triplet // between 23 and 46 L = 23; R = 46; possibleTripletInRange(L, R); } }    // This code is contributed // by anuj_67.

## Python3

 # Python3 program to find a non transitive  # co-prime triplets between L and R     # Checks if any possible triplet (a, b, c)  # satifying the condition that (a, b) is # coprime, (b, c) is coprime but (a, c) isnt  def possibleTripletInRange(L, R):        flag = False;     possibleA = 0;     possibleB = 0;     possibleC = 0;        numbersInRange = (R - L + 1);        # Case 1 : Less than 3 numbers     # between L and R      if (numbersInRange < 3):         flag = False;        # Case 2: More than 3 numbers      # between L and R      elif (numbersInRange > 3):         flag = True;            # triplets should always be of          # form (2k, 2k + 1, 2k + 2)         if ((L % 2) > 0):             L += 1;            possibleA = L;         possibleB = L + 1;         possibleC = L + 2;        else:                    # Case 3.1: Exactly 3 numbers in range         #            of form (2k, 2k + 1, 2k + 2)         if ((L % 2) == 0):             flag = True;             possibleA = L;             possibleB = L + 1;             possibleC = L + 2;         else:                            # Case 3.2: Exactly 3 numbers in range              #            of form (2k - 1, 2k, 2k + 1)              flag = False;        # flag = True indicates that a pair      # exists between L and R     if (flag == True):         print("(", possibleA, ",", possibleB,                ",", possibleC, ") is one such",                "possible triplet between", L, "and", R);     else:         print("No Such Triplet exists between",                                    L, "and", R);    # Driver code    # finding possible Triplet  # between 2 and 10 L = 2; R = 10; possibleTripletInRange(L, R);    # finding possible Triplet # between 23 and 46 L = 23; R = 46; possibleTripletInRange(L, R);    # This code is contributed by mits

## C#

 // C#  program to find a  // non transitive co-prime  // triplets between L and R  using System;    public class GFG{               // Checks if any possible triplet  // (a, b, c) satifying the condition  // that (a, b) is coprime, (b, c)  // is coprime but (a, c) isnt  static void possibleTripletInRange(int L,                                  int R)  {      bool flag = false;      int possibleA = 0,          possibleB = 0,          possibleC = 0;         int numbersInRange = (R - L + 1);         // Case 1 : Less than 3      // numbers between L and R      if (numbersInRange < 3)      {          flag = false;      }         // Case 2: More than 3      // numbers between L and R      else if (numbersInRange > 3)      {          flag = true;             // triplets should always          // be of form (2k, 2k + 1,          // 2k + 2)          if (L % 2 > 0)          {              L++;          }             possibleA = L;          possibleB = L + 1;          possibleC = L + 2;      }         else     {          /* Case 3.1: Exactly 3 numbers                      in range of form                      (2k, 2k + 1, 2k + 2) */         if (!(L % 2 > 0))          {              flag = true;              possibleA = L;              possibleB = L + 1;              possibleC = L + 2;          }          else         {              /* Case 3.2: Exactly 3 numbers                          in range of form                          (2k - 1, 2k, 2k + 1) */             flag = false;          }      }         // flag = True indicates      // that a pair exists      // between L and R      if (flag == true)      {              Console.WriteLine("(" + possibleA +                          ", " + possibleB +                          ", " + possibleC +              ")" + " is one such possible" +                      " triplet between " +                          L + " and " + R );      }      else {          Console.WriteLine("No Such Triplet" +                          " exists between " +                              L + " and " + R);      }  }     // Driver code         static public void Main (){            int L, R;      // finding possible Triplet      // between 2 and 10      L = 2;      R = 10;      possibleTripletInRange(L, R);      // finding possible Triplet      // between 23 and 46      L = 23;      R = 46;      possibleTripletInRange(L, R);      }  }  // This code is contributed by ajit

## PHP



Output:

(2, 3, 4) is one such possible triplet between 2 and 10
(24, 25, 26) is one such possible triplet between 24 and 46

Time complexity of this method is O(1).

My Personal Notes arrow_drop_up

Check out this Author's contributed articles.

If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

Please Improve this article if you find anything incorrect by clicking on the "Improve Article" button below.