Longest prefix that contains same number of X and Y in an array - GeeksforGeeks

Longest prefix that contains same number of X and Y in an array - GeeksforGeeks
Given two positive integers X and Y, and an array arr[] of positive integers. We need to find the longest prefix index which contains an equal number of X and Y. Print the maximum index of largest prefix if exist otherwise print -1.

We start from the index 0 and run a loop till the end of array. We keep increasing counters for both numbers X and Y. After iterating over the whole array, the last index when counts of X and y were equal is our result.

int findIndex(int arr[], int X, int Y, int n)

{

    // counters for X and Y

    int nx = 0,ny = 0;

 

    int result = -1;

    for (int i=0; i<n; i++)

    {

        // If value is equal to X increment counter of X

        if (arr[i]==X)

            nx++;

 

        // If value is equal to X increment counter of X

        if (arr[i]==Y)

            ny++;

 

        // If counters are equal(but not zero) save

        // the result as i

        if ((nx==ny) && (nx!=0 && ny!=0))

            result = i;

    }

    return result;

}

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