Question

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

Answer 1

function getEquilibriumIndex(arr) {
    let sum_arr = 0;
    let left_part_sum = 0;
    const size = arr.length;
    
    for (let i = 0 ; i < size; i++) {
        sum_arr += arr[i];
    }
    
    for (let i = 0; i < size; i++) {
        sum_arr -= arr[i];
        if (left_part_sum == sum_arr) {
            return i;
        }
        left_part_sum += arr[i];
    }
    
    return -1;
}


const arr = [-9, 2, 5, 8, -7, 4, 1];

console.log("equilibrium index = " + getEquilibriumIndex(arr));





/*
run:

equilibrium index = 3

*/

 

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