feat(leetcode): 907. Sum of Subarray Minimums : 单调栈

Author: upupming

leetcode/残酷刷题/907. Sum of Subarray Minimums.js

@@ -0,0 +1,23 @@
+/**
+ * @param {number[]} arr
+ * @return {number}
+ */
+const sumSubarrayMins = function (arr) {
+  const n = arr.length
+  arr[-1] = arr[n] = -1
+  let s = [-1]; const l = []; const r = []; let ans = 0
+  for (let i = 0; i < n; i++) {
+    while (arr[s[s.length - 1]] >= arr[i]) s.pop()
+    l[i] = s[s.length - 1]
+    s.push(i)
+  }
+  s = [n]
+  for (let i = n - 1; i >= 0; i--) {
+    while (arr[s[s.length - 1]] > arr[i]) s.pop()
+    r[i] = s[s.length - 1]
+    s.push(i)
+
+    ans = (ans + arr[i] * (i - l[i]) * (r[i] - i)) % (1e9 + 7)
+  }
+  return ans
+}