add code

Author: ncdhz

code/907.子数组的最小值之和.java

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+import java.util.ArrayDeque;
+import java.util.Deque;
+
+/*
+ * @lc app=leetcode.cn id=907 lang=java
+ *
+ * [907] 子数组的最小值之和
+ */
+
+// @lc code=start
+class Solution {
+ 
+ static int mod = 1000000007; 
+
+ public int sumSubarrayMins(int[] arr) {
+ 
+ int[] ls = new int[arr.length];
+ int[] rs = new int[arr.length];
+ Deque<Integer> ds = new ArrayDeque<Integer>();
+
+ for (int i = 0; i < arr.length; i++) {
+ while (!ds.isEmpty() && arr[i] <= arr[ds.peek()]) {
+ ds.pop();
+ }
+ 
+ ls[i] = i - (!ds.isEmpty() ? ds.peek(): -1);
+ ds.push(i);
+ }
+
+ ds.clear();
+ for (int i = arr.length - 1; i >= 0; i--) {
+ while(!ds.isEmpty() && arr[i] < arr[ds.peek()]) {
+ ds.pop();
+ }
+ rs[i] = (!ds.isEmpty() ? ds.peek() : arr.length) - i;
+ ds.push(i);
+ }
+
+ long result = 0;
+
+ for (int i = 0; i < rs.length; i++) {
+ result += (long)ls[i] * rs[i] * arr[i];
+ result %= mod;
+ }
+
+ return (int) result;
+ }
+}
+// @lc code=end
+