Create 1918-kth-smallest-subarray-sum.js

Author: everthis

1918-kth-smallest-subarray-sum.js

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+/**
+ * @param {number[]} nums
+ * @param {number} k
+ * @return {number}
+ */
+const kthSmallestSubarraySum = function(nums, k) {
+  const sum = nums.reduce((ac, e) => ac + e, 0), n = nums.length
+  let l = 0, r = sum
+  while(l < r) {
+    const mid = l + ((r - l) >> 1)
+    let cnt = 0
+    for(let i = 0, j = 0, tmp = 0; i < n; i++) {
+      tmp += nums[i]
+      while(tmp > mid) tmp -= nums[j++]
+      cnt += i - (j - 1)
+    }
+    if (cnt < k) l = mid + 1
+    else r = mid
+  }
+  return l
+};