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

function largestRectangleArea(heights: number[]): number {
    let stack = []
    let nextSmall = new Array(heights.length).fill(heights.length)
    let prevSmall = new Array(heights.length).fill(-1)
    for (let i = 0; i < heights.length; i++) {
        while (stack.length !== 0 && heights[stack[stack.length - 1]] > heights[i]) {
            nextSmall[stack[stack.length - 1]] = i
            stack.pop()
        }
        if (stack.length !== 0) {
            prevSmall[i] = stack[stack.length - 1]
        }
        stack.push(i)
    }
    let maxArea = 0
    for (let i = 0; i < heights.length; i++) {
        let currentArea = heights[i] * (nextSmall[i] - prevSmall[i] - 1)
        maxArea = Math.max(maxArea, currentArea)
    }
    return maxArea
}

export { largestRectangleArea }

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