Leetcode 724: Find Pivot Index (前缀和数组简单题)

  1. Find Pivot Index
    Easy

Given an array of integers nums, calculate the pivot index of this array.

The pivot index is the index where the sum of all the numbers strictly to the left of the index is equal to the sum of all the numbers strictly to the index's right.

If the index is on the left edge of the array, then the left sum is 0 because there are no elements to the left. This also applies to the right edge of the array.

Return the leftmost pivot index. If no such index exists, return -1.

Example 1:

Input: nums = [1,7,3,6,5,6]

Output: 3

Explanation:

The pivot index is 3.

Left sum = nums[0] + nums[1] + nums[2] = 1 + 7 + 3 = 11

Right sum = nums[4] + nums[5] = 5 + 6 = 11

Example 2:

Input: nums = [1,2,3]

Output: -1

Explanation:

There is no index that satisfies the conditions in the problem statement.

Example 3:

Input: nums = [2,1,-1]

Output: 0

Explanation:

The pivot index is 0.

Left sum = 0 (no elements to the left of index 0)

Right sum = nums[1] + nums[2] = 1 + -1 = 0

Constraints:

1 <= nums.length <= 104

-1000 <= nums[i] <= 1000

Note: This question is the same as 1991: https://leetcode.com/problems/find-the-middle-index-in-array/

解法1:前缀和数组

cpp 复制代码
class Solution {
public:
    int pivotIndex(vector<int>& nums) {
        int n = nums.size();
        vector<int> presums(n + 1, 0);
        for (int i = 1; i <= n; i++) presums[i] = presums[i - 1] + nums[i - 1];
        
        for (int i = 1; i <= n; i++) {
            if (presums[i - 1] == presums[n] - presums[i]) return i - 1;
        }
        return -1;
    } 
};
相关推荐
小刘鸭地下城2 分钟前
哈希表核心精要:从 O(1) 原理到链式地址与开放寻址
算法
今后12320 分钟前
【数据结构】二叉树的概念
数据结构·二叉树
BenChuat25 分钟前
Java常见排序算法实现
java·算法·排序算法
元亓亓亓1 小时前
LeetCode热题100--105. 从前序与中序遍历序列构造二叉树--中等
算法·leetcode·职场和发展
纪元A梦1 小时前
贪心算法在SDN流表优化中的应用
算法·贪心算法
JCBP_1 小时前
QT(4)
开发语言·汇编·c++·qt·算法
码熔burning1 小时前
JVM 垃圾收集算法详解!
jvm·算法
小柴狗2 小时前
C语言关键字详解:static、const、volatile
算法
仙俊红4 小时前
LeetCode每日一题,20250914
算法·leetcode·职场和发展
风中的微尘10 小时前
39.网络流入门
开发语言·网络·c++·算法