Given a string of 0 and 1, we need to check that the given string is valid or not. The given string is valid when there is no zero is present in between 1’s. For example, 1111, 0000111110, 1111000 are valid strings but 01010011, 01010, 101 are not.
One approach to solving the problem is discussed here, other using Regular expressions is given Set 2
Examples:
Input : 100 Output : VALID Input : 1110001 Output : NOT VALID There is 0 between 1s Input : 00011 Output : VALID
Algorithm:
- Find the first occurrence of 1 in the string. Let it be first.
- Find the last occurrence of 1 in the string. Let it be last.
- Run a loop from first to last and return false if there is a 0. If no 0 found, return true.
Explanation: Suppose we have a string: 01111011110000 Now take two variables say A and B. run a loop for 0 to length of the string and point A to the first occurrence of 1, after that again run a loop from length of the string to 0 and point second variable to the last occurrence of 1. So A = 1 (Position of first '1' is the string) and B = 9 (last occurrence of '1'). Now run a loop from A to B and check that '0' is present between 1 or not, if "YES" than set flag to 1 and break the loop, else set flag to 0. In this case flag will set to 1 as the given string is not valid and print "NOT VALID".
C++
// C++ program to check if a string is valid or not. #include <bits/stdc++.h> using namespace std; // Function returns 1 when string is valid // else returns 0 bool checkString(string s) { int len = s.length(); // Find first occurrence of 1 in s[] int first = s.size() + 1; for (int i = 0; i < len; i++) { if (s[i] == '1') { first = i; break; } } // Find last occurrence of 1 in s[] int last = 0; for (int i = len - 1; i >= 0; i--) { if (s[i] == '1') { last = i; break; } } // Check if there is any 0 in range for (int i = first; i <= last; i++) if (s[i] == '0') return false; return true; } // Driver code int main() { string s = "00011111111100000"; checkString(s) ? cout << "VALID\n" : cout << "NOT VALID\n"; return 0; } |
Java
// Java program to check if a string is valid or not. class Test { // Method returns 1 when string is valid // else returns 0 static boolean checkString(String s) { int len = s.length(); // Find first occurrence of 1 in s[] int first = 0; for (int i = 0; i < len; i++) { if (s.charAt(i) == '1') { first = i; break; } } // Find last occurrence of 1 in s[] int last = 0; for (int i = len - 1; i >= 0; i--) { if (s.charAt(i) == '1') { last = i; break; } } // Check if there is any 0 in range for (int i = first; i <= last; i++) if (s.charAt(i) == '0') return false; return true; } // Driver method public static void main(String args[]) { String s = "00011111111100000"; System.out.println(checkString(s) ? "VALID" : "NOT VALID"); } } |
Python
# Python3 program to check if # a string is valid or not. # Function returns 1 when # string is valid else # returns 0 def checkString(s): Len = len(s) # Find first occurrence # of 1 in s[] first = len(s) + 1 for i in range(Len): if(s[i] == '1'): first = i break # Find last occurrence # of 1 in s[] last = 0 for i in range(Len - 1, -1, -1): if(s[i] == '1'): last = i break # Check if there is any # 0 in range for i in range(first, last + 1): if(s[i] == '0'): return False return True # Driver code s = "00011111111100000"if(checkString(s)): print("VALID") else: print("NOT VALID") # This code is contributed by avanitrachhadiya2155 |
C#
// C# program to check if a // string is valid or not. using System; class GFG { // Method returns 1 when string is valid // else returns 0 static bool checkString(String s) { int len = s.Length; // Find first occurrence of 1 in s[] int first = 0; for (int i = 0; i < len; i++) { if (s[i] == '1') { first = i; break; } } // Find last occurrence of 1 in s[] int last = 0; for (int i = len - 1; i >= 0; i--) { if (s[i] == '1') { last = i; break; } } // Check if there is any 0 in range for (int i = first; i <= last; i++) if (s[i] == '0') return false; return true; } // Driver method public static void Main() { string s = "00011111111100000"; Console.WriteLine(checkString(s) ? "VALID" : "NOT VALID"); } } // This code is contributed by Sam007 |
Output:
VALID
Time Complexity: O(n)
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