For example,
Given height = [2,1,5,6,2,3],
return 10.
解题思路：
参考Problem H: Largest Rectangle in a Histogram第四种思路，或者翻译版Largest Rectangle in Histogram@LeetCode，JAVA实现如下：
public int largestRectangleArea(int[] height) {
Stack<Integer> stk = new Stack<Integer>();
int ret = 0;
for (int i = 0; i <= height.length; i++) {
int h=0;
if(i<height.length)
h=height[i];
if (stk.isEmpty() || h >= height[stk.peek()])
stk.push(i);
else {
int top = stk.pop();
ret = Math.max(ret, height[top] * (stk.empty() ? i : i - stk.peek() - 1));
i--;
}
}
return ret;
}