add sol

leetcode/907.SumofSubarrayMinimums/sumofSubarrayMinimums.go

@@ -0,0 +1,55 @@
+// https://leetcode.com/problems/sum-of-subarray-minimums
+
+package main
+
+import (
+	"fmt"
+)
+
+func sumSubarrayMins(arr []int) int {
+	const mod int = 1e9 + 7
+
+	n := len(arr)
+	left := make([]int, n)
+	right := make([]int, n)
+	for i := range left {
+		left[i] = -1
+		right[i] = n
+	}
+
+	stk := []int{}
+	for i, v := range arr {
+		for len(stk) > 0 && arr[stk[len(stk)-1]] >= v {
+			stk = stk[:len(stk)-1]
+		}
+		if len(stk) > 0 {
+			left[i] = stk[len(stk)-1]
+		}
+		stk = append(stk, i)
+	}
+
+	stk = []int{}
+	for i := n - 1; i >= 0; i-- {
+		for len(stk) > 0 && arr[stk[len(stk)-1]] > arr[i] {
+			stk = stk[:len(stk)-1]
+		}
+		if len(stk) > 0 {
+			right[i] = stk[len(stk)-1]
+		}
+		stk = append(stk, i)
+	}
+
+	result := 0
+	for i, v := range arr {
+		result += (i - left[i]) * (right[i] - i) * v % mod
+		result %= mod
+	}
+
+	return result
+}
+
+func main() {
+	arr := []int{11, 81, 94, 43, 3}
+
+	fmt.Println(sumSubarrayMins(arr))
+}