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subarraySumEqualsK.js
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41 lines (32 loc) · 1.01 KB
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/**
* LeetCode 560. Subarray Sum Equals K
* https://leetcode.com/problems/subarray-sum-equals-k/
*
* Given an array of integers nums and an integer k, return the total number
* of subarrays whose sum equals to k.
*
* A subarray is a contiguous non-empty sequence of elements within an array.
*/
/**
* @param {number[]} nums
* @param {number} k
* @return {number}
*/
function subarraySumEqualsK(nums, k) {
const prefixSumCounts = new Map();
prefixSumCounts.set(0, 1);
let totalSubarrays = 0;
let runningSum = 0;
for (const num of nums) {
runningSum += num;
// The value we need to have seen previously to make the current subarray sum to k
const targetPreviousSum = runningSum - k;
if (prefixSumCounts.has(targetPreviousSum)) {
totalSubarrays += prefixSumCounts.get(targetPreviousSum);
}
const currentCount = prefixSumCounts.get(runningSum) || 0;
prefixSumCounts.set(runningSum, currentCount + 1);
}
return totalSubarrays;
}
module.exports = { subarraySumEqualsK };