LeetCode-in-All

84. Largest Rectangle in Histogram

Hard

Given an array of integers heights representing the histogram’s bar height where the width of each bar is 1, return the area of the largest rectangle in the histogram.

Example 1:

Input: heights = [2,1,5,6,2,3]

Output: 10

Explanation: The above is a histogram where width of each bar is 1. The largest rectangle is shown in the red area, which has an area = 10 units.

Example 2:

Input: heights = [2,4]

Output: 4

Constraints:

• 1 <= heights.length <= 105
• 0 <= heights[i] <= 104

Solution

# @param {Integer[]} heights
# @return {Integer}
def largest_rectangle_area(heights)
  area = 0
  stack = []
  return 0 if heights.empty?
  return heights[0] * heights.length if heights.uniq.length == 1

  heights.each.with_index do |height, index|
    start = index
    while !stack.empty? && stack.last[1] > height do
      i, h = stack.pop
      area = [area, h * (index - i)].max
      start = i
    end
    stack << [start, height]
  end

  stack.each do |i, s|
    area = [area, s * (heights.length - i)].max
  end

  area
end

This site is open source. Improve this page.