@@ -228,6 +228,50 @@ class Solution {
228228}
229229```
230230
231+ 单调栈
232+ ``` java
233+ class Solution {
234+ int largestRectangleArea (int [] heights ) {
235+ Stack<Integer > st = new Stack<Integer > ();
236+ 237+ // 数组扩容,在头和尾各加入一个元素
238+ int [] newHeights = new int [heights. length + 2 ];
239+ newHeights[0 ] = 0 ;
240+ newHeights[newHeights. length - 1 ] = 0 ;
241+ for (int index = 0 ; index < heights. length; index++ ){
242+ newHeights[index + 1 ] = heights[index];
243+ }
244+ 245+ heights = newHeights;
246+ 247+ st. push(0 );
248+ int result = 0 ;
249+ // 第一个元素已经入栈,从下表1开始
250+ for (int i = 1 ; i < heights. length; i++ ) {
251+ // 注意heights[i] 是和heights[st.top()] 比较 ,st.top()是下表
252+ if (heights[i] > heights[st. peek()]) {
253+ st. push(i);
254+ } else if (heights[i] == heights[st. peek()]) {
255+ st. pop(); // 这个可以加,可以不加,效果一样,思路不同
256+ st. push(i);
257+ } else {
258+ while (heights[i] < heights[st. peek()]) { // 注意是while
259+ int mid = st. peek();
260+ st. pop();
261+ int left = st. peek();
262+ int right = i;
263+ int w = right - left - 1 ;
264+ int h = heights[mid];
265+ result = Math . max(result, w * h);
266+ }
267+ st. push(i);
268+ }
269+ }
270+ return result;
271+ }
272+ }
273+ ```
274+ 231275Python:
232276
233277动态规划
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