Create kth-smallest-subarray-sum.cpp

Author: kamyu104

C++/kth-smallest-subarray-sum.cpp

@@ -0,0 +1,32 @@
+// Time:  O(nlogr)
+// Space: O(1)
+
+class Solution {
+public:
+    int kthSmallestSubarraySum(vector<int>& nums, int k) {
+        int left = *min_element(cbegin(nums), cend(nums));
+        int right = accumulate(cbegin(nums), cend(nums), 0);
+        while (left <= right) {
+            const auto& mid = left + (right - left) / 2;
+            if (check(nums, k, mid)) {
+                right = mid - 1;
+            } else {
+                left = mid + 1;
+            }
+        }
+        return left;
+    }
+
+private:
+    bool check(const vector<int>& nums, int k, int x) {
+        int cnt = 0, curr = 0, left = 0;
+        for (int right = 0; right < size(nums); ++right) {
+            curr += nums[right];
+            while (curr > x) {
+                curr -= nums[left++];
+            }
+            cnt += right - left + 1;
+        }
+        return cnt >= k;
+    }
+};