Leetcode724 Find Pivot Index（數組的中間下標）

題目

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.

Note:

The length of nums will be in the range [0, 10000].Each element nums[i] will be an integer in the range [-1000, 1000].

分析

注意所給數組元素的爲整數類型的，其中有正有負

java實現

class Solution {
    public int pivotIndex(int[] nums) {
        int len = nums.length;
        int sum = 0;
        int lsum = 0;
        for(int x:nums){
            sum+=x;
        }
        for(int i = 0;i<len;i++){
            lsum += nums[i];
            if(lsum == sum - lsum + nums[i] ){
                return i;
            }
        }
        
        return -1;
    }
}

js實現

/**
 * @param {number[]} nums
 * @return {number}
 */
var pivotIndex = function(nums) {
    var len = nums.length;
    var sum = 0;
    var lsum = 0;
    
    for(var x in nums){//for-in循環遍歷數組時，x存放的是下標信息
        sum+=nums[x];
    }
    
    for(var i= 0;i<len;i++){
        lsum += nums[i];
        if(lsum == sum - lsum + nums[i]){
            return i;
        }
    }
    
    return -1;
};