Leetcode 84: Largest Rectangle in Histogram

Posted 2020-10-14 Keep walking

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 heights = [2,1,5,6,2,3],
return 10.

 

Note: this problem is pretty tricky, I could not solve it by myself in O(n) time.

 1 public class Solution {
 2     public int LargestRectangleArea(int[] heights) {
 3         Stack<int> stack = new Stack<int>();
 4         int i = 0, maxArea = 0;
 5              
 6         while (i <= heights.Length)
 7         {
 8             var h = i == heights.Length ? 0 : heights[i];
 9             if (stack.Count == 0 || h >= heights[stack.Peek()])
10             {
11                 stack.Push(i);
12                 i++;
13             }
14             else
15             {
16                 var left = stack.Pop();
17                 
18                 maxArea = Math.Max(maxArea, stack.Count == 0 ? heights[left] * i : heights[left] * (i - stack.Peek() - 1));
19             }
20         }
21         
22         return maxArea;
23     }
24 }