add: 和为K的子数组

.vscode/settings.json

@@ -14,6 +14,7 @@
     "nums",
     "powx",
     "pwwkew",
+    "subarray",
     "umghlrlose",
     "xuan",
     "zhong",

README.md

@@ -340,6 +340,11 @@ LeetCode 与 LintCode 解题记录。此为个人练习仓库，代码中对重
   - LeetCode 50. Pow(x, n) <https://leetcode-cn.com/problems/powx-n/>
   - LintCode 428. x的n次幂 <https://www.lintcode.com/problem/powx-n/>
 
+- [和为K的子数组](src/math/subarray-sum-equals-k.js)
+
+  - LeetCode 560. 和为K的子数组 <https://leetcode-cn.com/problems/subarray-sum-equals-k/>
+  - LintCode 838. 子数组和为K <https://www.lintcode.com/problem/subarray-sum-equals-k/>
+
 ## 堆
 
 - [超级丑数](src/stack/super-ugly-number.js)【未完成】

src/math/subarray-sum-equals-k.js

@@ -0,0 +1,25 @@
+/**
+ * @param {number[]} nums
+ * @param {number} k
+ * @return {number}
+ */
+export const subarraySum = function (nums, k) {
+  const map = new Map()
+  let sum = 0
+  let res = 0
+
+  nums.forEach((n, index) => {
+    sum += n
+    if (sum === k) res++
+    const subSum = sum - k
+    let value = []
+    if (map.has(subSum)) res += map.get(subSum).length
+    if (map.has(sum)) {
+      value = map.get(sum)
+    }
+    value.push(index)
+    map.set(sum, value)
+  })
+
+  return res
+}

test/math/subarray-sum-equals-k.test.js

@@ -0,0 +1,5 @@
+import { subarraySum } from '../../src/math/subarray-sum-equals-k'
+
+test('和为K的子数组', () => {
+  expect(subarraySum([1, 1, 1], 2)).toBe(2)
+})