Generate an alternate increasing and decreasing Array

Given a string str of size N containing two types of character only that are “I” or “D”. The task is to generate an array arr[0, 1, . . N] of size N + 1 satisfying the following conditions: 

• If str[i] == “I”   then   arr[i] < arr[i+1]
• If str[i] == “D”  then  arr[i] > arr[i+1]

Examples:

Input: str = “IDID” 
Output: 0 4 1 3 2 
Explanation:
str[0] == “I” therefore arr[0] < arr[1] 
str[1] == “D” therefore arr[1] > arr[2] 
str[2] == “I” therefore arr[2] < arr[3] 
str[3] == “D” therefore arr[3] > arr[4]

Input: str = “III” 
Output: 0 1 2 3

Approach:

1. Initialize variable START as 0 and END as N.
2. Iterate over the entire array.
3. If str[i] == “I”  then assign START at arr[i] and Increment the START.
4. If str[i] == “D” then assign END at arr[i] and Decrement the END.
5. Now the last element of the array isn’t assigned so assign START at A[N].

Below is the implementation of the approach.  

C++

// C++ program to Generate an increasing
// and decreasing array

#include <iostream>
using namespace std;

// Function that returns generated array
int* DiStirngMatch(string Str)
{
    int N = Str.length();

    // Dynamically allocate array
    int* arr = new int[N];

    // START=0, END=N
    int START = 0, END = N;

    // iterate over array
    for (int i = 0; i < N; i++) {

        // if Str[i]=='I' assign arr[i]
        // as START and increment START
        if (Str[i] == 'I')
            arr[i] = START++;

        // if str[i]=='D' assign arr[i]
        // as END and decrement END
        if (Str[i] == 'D')
            arr[i] = END--;
    }

    // assign A[N] as START
    arr[N] = START;

    // return starting
    // address of array A
    return arr;
}

// Driver Program
int main()
{
    string Str = "IDID";
    int N = Str.length();
    int* ptr = DiStirngMatch(Str);
    for (int i = 0; i <= N; i++)
        cout << ptr[i] << " ";

    return 0;
}

Java

// Java program to generate an increasing
// and decreasing array
class GFG{

// Function that returns generated array
static int []DiStirngMatch(String Str)
{
    int N = Str.length();

    // Dynamically allocate array
    int []arr = new int[N + 1];

    // START=0, END=N
    int START = 0, END = N;

    // Iterate over array
    for(int i = 0; i < N; i++)
    {

        // if Str[i]=='I' assign arr[i]
        // as START and increment START
        if (Str.charAt(i) == 'I')
            arr[i] = START++;

        // if str[i]=='D' assign arr[i]
        // as END and decrement END
        if (Str.charAt(i) == 'D')
            arr[i] = END--;
    }

    // Assign A[N] as START
    arr[N] = START;

    // Return starting
    // address of array A
    return arr;
}

// Driver code
public static void main(String[] args)
{
    String Str = "IDID";
    int N = Str.length();
    int[] ptr = DiStirngMatch(Str);

    for(int i = 0; i <= N; i++)
        System.out.print(ptr[i] + " ");
}
}

// This code is contributed by amal kumar choubey

Python3

# Python3 program to generate an
# increasing and decreasing array

# Function that returns generated array
def DiStirngMatch(Str):

    N = len(Str)

    # Dynamically allocate array
    arr = (N + 1) * [0]

    # START, END= 0 ,N
    START, END = 0, N

    # Iterate over array
    for i in range (N):

        # If Str[i]=='I' assign arr[i]
        # as START and increment START
        if (Str[i] == 'I'):
            arr[i] = START
            START += 1

        # If str[i]=='D' assign arr[i]
        # as END and decrement END
        if (Str[i] == 'D'):
            arr[i] = END
            END -= 1

    # Assign A[N] as START
    arr[N] = START

    # Return starting
    # address of array A
    return arr

# Driver code
if __name__ == "__main__":

    Str = "IDID"
    N = len(Str)
    ptr = DiStirngMatch(Str)

    for i in range (N + 1):
        print(ptr[i], end = " ")

# This code is contributed by chitranayal

C#

// C# program to generate an increasing
// and decreasing array
using System;

class GFG{

// Function that returns generated array
static int []DiStirngMatch(String Str)
{
    int N = Str.Length;

    // Dynamically allocate array
    int []arr = new int[N + 1];

    // START=0, END=N
    int START = 0, END = N;

    // Iterate over array
    for(int i = 0; i < N; i++)
    {

        // if Str[i]=='I' assign arr[i]
        // as START and increment START
        if (Str[i] == 'I')
            arr[i] = START++;

        // if str[i]=='D' assign arr[i]
        // as END and decrement END
        if (Str[i] == 'D')
            arr[i] = END--;
    }

    // Assign A[N] as START
    arr[N] = START;

    // Return starting
    // address of array A
    return arr;
}

// Driver code
public static void Main(String[] args)
{
    String Str = "IDID";
    int N = Str.Length;
    int[] ptr = DiStirngMatch(Str);

    for(int i = 0; i <= N; i++)
        Console.Write(ptr[i] + " ");
}
}

// This code is contributed by amal kumar choubey

Javascript

<script>

// Javascript program to Generate an increasing
// and decreasing array

// Function that returns generated array
function DiStirngMatch( Str)
{
    var N = Str.length;

    // Dynamically allocate array
    var arr = Array(N).fill(0);

    // START=0, END=N
    var START = 0, END = N;

    // iterate over array
    for (var i = 0; i < N; i++) {

        // if Str[i]=='I' assign arr[i]
        // as START and increment START
        if (Str[i] == 'I')
            arr[i] = START++;

        // if str[i]=='D' assign arr[i]
        // as END and decrement END
        if (Str[i] == 'D')
            arr[i] = END--;
    }

    // assign A[N] as START
    arr[N] = START;

    // return starting
    // address of array A
    return arr;
}

// Driver Program
var Str = "IDID";
var N = Str.length;
var ptr = DiStirngMatch(Str);
for (var i = 0; i <= N; i++)
    document.write( ptr[i] + " ");

// This code is contributed by itsok.
</script>

Output:

0 4 1 3 2

Time Complexity: O (N)
Auxiliary Space: O (N)