添加0084.柱状图中最大的矩形java动态规划解法

problems/0084.柱状图中最大的矩形.md

@@ -195,6 +195,40 @@ public:
 
 Java: 
 
+动态规划
+```java
+class Solution {
+    public int largestRectangleArea(int[] heights) {
+        int length = heights.length;
+        int[] minLeftIndex = new int [length];
+        int[] maxRigthIndex = new int [length];
+
+        // 记录左边第一个小于该柱子的下标
+        minLeftIndex[0] = -1 ;
+        for (int i = 1; i < length; i++) {
+            int t = i - 1;
+            // 这里不是用if，而是不断向右寻找的过程
+            while (t >= 0 && heights[t] >= heights[i]) t = minLeftIndex[t];
+            minLeftIndex[i] = t;
+        }
+        // 记录每个柱子 右边第一个小于该柱子的下标
+        maxRigthIndex[length - 1] = length;
+        for (int i = length - 2; i >= 0; i--) {
+            int t = i + 1;
+            while(t < length && heights[t] >= heights[i]) t = maxRigthIndex[t];
+            maxRigthIndex[i] = t;
+        }
+        // 求和
+        int result = 0;
+        for (int i = 0; i < length; i++) {
+            int sum = heights[i] * (maxRigthIndex[i] - minLeftIndex[i] - 1);
+            result = Math.max(sum, result);
+        }
+        return result;
+    }
+}
+```
+
 Python:
 
 动态规划