Question

I was solving a question, with which I am having some problems:

Complete the function getEqualSumSubstring, which takes a single argument. The single argument is a string s, which contains only non-zero digits.
This function should print the length of longest contiguous substring of s, such that the length of the substring is 2*N digits and the sum of the leftmost N digits is equal to the sum of the rightmost N digits. If there is no such string, your function should print 0.

int getEqualSumSubstring(string s) {
int i=0,j=i,foundLength=0;
    for(i=0;i<s.length();i++)
    {
        for(j=i;j<s.length();j++)
        {
            int temp = j-i;
            if(temp%2==0)
            {
                int leftSum=0,rightSum=0;
                string tempString=s.substr(i,temp);
                for(int k=0;k<temp/2;k++)
                {
                    leftSum=leftSum+tempString[k]-'0';
                    rightSum=rightSum+tempString[k+(temp/2)]-'0';
                }
                if((leftSum==rightSum)&&(leftSum!=0))
                    if(s.length()>foundLength)
                    foundLength=s.length(); 
            }
        }
    }
    return(foundLength);

}

The problem is that this code is working for some samples and not for the others. Since this is an exam type question I don’t have the test cases either.

Answer 1

This code works

int getEqualSumSubstring(string s) {
    int i=0,j=i,foundLength=0;
    for(i=0;i<s.length();i++)
    {
        for(j=i;j<s.length();j++)
        {
            int temp = j-i+1;

            if(temp%2==0)
            {
                int leftSum=0,rightSum=0;
                string tempString=s.substr(i,temp);
                // printf("%d ",tempString.length());
                for(int k=0;k<temp/2;k++)
                {
                    leftSum=leftSum+tempString[k]-48;
                    rightSum=rightSum+tempString[k+(temp/2)]-48;
                }
                if((leftSum==rightSum)&&(leftSum!=0))
                    if(tempString.length()>foundLength)
                    foundLength=tempString.length(); 
            }
        }
    }
    return(foundLength);
}

The temp variable must be j-i+1. Otherwise the case where the whole string is the answer will not be covered. Also, we need to make the change suggested by Scott.