Find Pivot Index Java Solution - The Coding Shala

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Find Pivot Index

Problem:
Given an array of integers nums, write a method that returns the "pivot" index of this array.

We define the pivot index as the index where the sum of the numbers to the left of the index is equal to the sum of the numbers to the right of the index.

If no such index exists, we should return -1. If there are multiple pivot indexes, you should return the left-most pivot index.

Example 1:

Input: 
nums = [1, 7, 3, 6, 5, 6]
Output: 3
Explanation: 
The sum of the numbers to the left of index 3 (nums[3] = 6) is equal to the sum of numbers to the right of index 3.
Also, 3 is the first index where this occurs.

Example 2:

Input: 
nums = [1, 2, 3]
Output: -1
Explanation: 
There is no index that satisfies the conditions in the problem statement.

Find Pivot Index Java Solution

Approach:

At every index, we can check if the total sum to its left and total sum to right of this index equals or not.

First, we will find the total sum of an array then using a loop every time we check if the sum till the current index-1 is equaled to the sum to the right side of this index.

Java Code:: 

class Solution {
    public int pivotIndex(int[] nums) {
        int len = nums.length;
        if(len<3) return -1;
        int right_sum = 0;
        //total sum
        for(int i=0; i<len; i++) right_sum += nums[i];
        
        int left_sum = 0;
        //checking sum
        for(int i=0;i<len;i++){
            right_sum -= nums[i]; //current index does not count
            if(left_sum == right_sum) return i;
            left_sum += nums[i];
        }
        
        return -1;
    }
}


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