Question

How to find the equilibrium index of an array (sum arr[0 to index - 1] == sum arr[index + 1 to size]) in C

Answer 1

#include <stdio.h>

int getEquilibriumIndex(int arr[], int size) {
    int sum_arr = 0;
    int left_part_sum = 0; 

    for (int i = 0; i < size; i++)
        sum_arr += arr[i];

    for (int i = 0; i < size; i++) {
        sum_arr -= arr[i];

        if (left_part_sum == sum_arr)
            return i;

        left_part_sum += arr[i];
    }

    return -1;
}

int main()
{
    int arr[] = { -9, 2, 5, 8, -7, 4, 1 };

    int size = sizeof(arr) / sizeof(arr[0]);

    printf("equilibrium index = %d", getEquilibriumIndex(arr, size));

    return 0;
}




/*
run:

equilibrium index = 3

*/

 

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