02-Pivot-Index.md

Pivot Index

Problem Link

https://leetcode.com/problems/find-pivot-index/

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Pattern

• Prefix Sum

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Approach

Compute total sum, then iterate tracking left sum. Pivot where left == total - left - nums[i].

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Time Complexity

O(n)

Space Complexity

O(1)

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Java Solution

class Solution {
    public int pivotIndex(int[] nums) {
        int total = 0;
        for (int n : nums) total += n;
        int left = 0;
        for (int i = 0; i < nums.length; i++) {
            if (left == total - left - nums[i]) return i;
            left += nums[i];
        }
        return -1;
    }
}