Largest Rectangle in Histogram leetcode java

题目：

Given n non-negative integers representing the histogram's bar
height where the width of each bar is 1, find the area of largest
rectangle in the histogram.

Above is a histogram where width of each bar is 1, given height = [2,1,5,6,2,3].

The largest rectangle is shown in the shaded area, which has area = 10 unit.

For example,
Given height = [2,1,5,6,2,3],
return 10.

题解：

这道题自己是完全没想到用栈了。。

有个很完整很详细很好的讲解在这里： http://www.cnblogs.com/lichen782/p/leetcode_Largest_Rectangle_in_Histogram.html

我就不写了。贴一下上面提到的代码吧。

O(n^2)的：

 1 public int largestRectangleArea(int[] height) {

 2         // Start typing your Java solution below

 3         // DO NOT write main() function

 4         int[] min = new int[height.length];

 5         int maxArea = 0;

 6         for(int i = 0; i < height.length; i++){

 7             if(height[i] != 0 && maxArea/height[i] >= (height.length - i)) {

 8                 continue;

 9             }

             for(int j = i; j < height.length; j++){

                 if(i == j) min[j] = height[j];

                 else {

                     if(height[j] < min[j - 1]) {

                         min[j] = height[j];

                     }else min[j] = min[j-1];

                 }

                 int tentativeArea = min[j] * (j - i + 1);

                 if(tentativeArea > maxArea) {

                     maxArea = tentativeArea;

                 }

             }

         }

         return maxArea;

     }

O(n)的：

 1 public int largestRectangleArea2(int[] height) {

 2         Stack<Integer> stack = new Stack<Integer>();

 3         int i = 0;

 4         int maxArea = 0;

 5         int[] h = new int[height.length + 1];

 6         h = Arrays.copyOf(height, height.length + 1);

 7         while(i < h.length){

 8             if(stack.isEmpty() || h[stack.peek()] <= h[i]){

 9                 stack.push(i++);

             }else {

                 int t = stack.pop();

                 maxArea = Math.max(maxArea, h[t] * (stack.isEmpty() ? i : i - stack.peek() - 1));

             }

         }

         return maxArea;

     }

巴特西

Largest Rectangle in Histogram leetcode java

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