LeetCode OJ-560.Subarray Sum Equals K

LeetCode OJ-560.Subarray Sum Equals K

题目描述

Given an array of integers and an integer k, you need to find the total number of continuous subarrays whose sum equals to k.

Example 1:

Input:nums = [1,1,1], k = 2
Output: 2

Note:

1. The length of the array is in range [1, 20,000].
2. The range of numbers in the array is [-1000, 1000] and the range of the integer k is [-1e7, 1e7].

题目理解

​ 给定一个k，在数组中求和为k的连续子数组有多少个。因为是连续的，可以两层循环直接遍历就行了。要注意一个点，遍历时当加到某个元素时，和刚好为k，这时候++cnt就好了，还应该继续遍历下去，直至到达数组尾部。

Code

class Solution {
public:
    int subarraySum(vector<int>& nums, int k) {
        int cnt = 0;
        int sz = (int) nums.size();
        int i, j;
        int sum;
        for (i = 0; i < sz; ++i) {
            sum = nums[i]; 
            if (sum == k) {
                ++cnt;
            }
            for (j = i + 1; j < sz; ++j) {
                sum += nums[j];
                if (sum == k) {
                    ++cnt;
                }
            }
        }

        return cnt;
    }
};