Last Index of One

Problem

Given a string S consisting only '0's and '1's, find the last index of the '1' present in it.

Examples:

Example 1:

Input:
S = 00001
Output:
4
Explanation:
Last index of  1 in given string is 4.

Example 2:

Input:
0
Output:
-1
Explanation:
Since, 1 is not present, so output is -1.

Your task:

You don't need to read input or print anything. Your task is to complete the function lastIndex() which takes the string S as inputs and returns the last index of '1'. If '1' is not present, return "-1" (without quotes).

• Expected Time Complexity: $O(N)$
• Expected Auxiliary Space: $O(1)$

Constraints:

• $1 <= |S| <= 10^6$
• $S = {0,1}$

Solution

Python

def lastIndex(self, s):
    index = -1
    for i in range(0, len(s)):
        if s[i] == '1':
            index = i
    return index

Java

public int lastIndex( String s) {
    int index = -1;
    for (int i = 0; i < s.length(); i++) {
        if (s.charAt(i) == '1') { 
            index = i;
        }
    }
    return index;
}

C++

int lastIndex(string s) {
    int index = -1;
    for (int i = 0; i < s.length(); i++) {
        if (s[i] == '1') { 
            index = i;
        }
    }
    return index; 
}

C

int lastIndex(const char *s) {
    int index = -1;
    int length = strlen(s);
    for (int i = 0; i < length; i++) {
        if (s[i] == '1') {  instead of integer 1
            index = i;
        }
    }
    return index;
}

• Time Complexity: $O(N)$
• Auxiliary Space: $O(1)$