[LeetCode] Largest Rectangle in Histogram

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

.

这个题就是求解 max ｛max｛以height[i] 为高的最大面积｝｝ 0 <= i < n

public class Solution {
public int largestRectangleArea(int[] height) {
if (height == null || height.length < 1) {
return 0;
}

int max = 0;
Stack<Integer> stack = new Stack<Integer>();
for (int i = 0; i < height.length; i++) {
while (!stack.isEmpty() && height[i] <= height[stack.peek()]) {
int curIndex = stack.pop();
int nowArea = 0;
if (stack.isEmpty()) {
nowArea = i * height[curIndex];
} else {
nowArea = (i - stack.peek() - 1) * height[curIndex];
}

if (nowArea > max) {
max = nowArea;
}
}

stack.push(i);
}

while (!stack.isEmpty()) {
int curIndex = stack.pop();
int nowArea = 0;
if (stack.isEmpty()) {
nowArea = (height.length) * height[curIndex];
} else {
nowArea = (height.length - stack.peek() - 1) * height[curIndex];
}

if (nowArea > max) {
max = nowArea;
}
}

return max;
}
}