560

560. Subarray Sum Equals K (Medium)

Given an array of integers nums and an integer k, return the total number of continuous subarrays whose sum equals to k.

 

Example 1:

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

Example 2:

Input: nums = [1,2,3], k = 3
Output: 2

 

Constraints:

• 1 <= nums.length <= 2 * 104
• -1000 <= nums[i] <= 1000
• -107 <= k <= 107

Companies:
Facebook, Amazon, Google, Oracle, ByteDance, Quora, tiktok, Microsoft, LinkedIn, Bloomberg, Apple, Snapchat, Expedia, Walmart Labs, Tesla, Paypal, Visa, DoorDash

Related Topics:
Array, Hash Table, Prefix Sum

Similar Questions:

• Two Sum (Easy)
• Continuous Subarray Sum (Medium)
• Subarray Product Less Than K (Medium)
• Find Pivot Index (Easy)
• Subarray Sums Divisible by K (Medium)
• Minimum Operations to Reduce X to Zero (Medium)
• K Radius Subarray Averages (Medium)

Solution 1. Prefix State Map

// OJ: https://leetcode.com/problems/subarray-sum-equals-k/
// Author: github.com/lzl124631x
// Time: O(N)
// Space: O(N)
class Solution {
public:
    int subarraySum(vector<int>& nums, int k) {
        int ans = 0, sum = 0;
        unordered_map<int, int> m{{0, 1}};
        for (int n : nums) {
            sum += n;
            auto it = m.find(sum - k);
            if (it != m.end()) ans += it->second;
            m[sum]++;
        }
        return ans;
    }
};