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84. Largest Rectangle in Histogram

HardOpen on LeetCodeProblem statement

Problem Statement

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:

C++

Source file
class Solution {
public:
 int largestRectangleArea(vector<int>& height) {
    if (height.empty() || height.size() == 0) {
        return 0;
    }
    int lessFromLeft[height.size()]; // idx of the first bar the left that is lower than current
    int lessFromRight[height.size()]; // idx of the first bar the right that is lower than current
    lessFromRight[height.size()-1] = height.size();
    lessFromLeft[0] = -1;

    for (int i = 1; i < height.size(); i++) {
        int p = i - 1;

        while (p >= 0 && height[p] >= height[i]) {
            p = lessFromLeft[p];
        }
        lessFromLeft[i] = p;
    }

    for (int i = height.size() - 2; i >= 0; i--) {
        int p = i + 1;

        while (p < height.size() && height[p] >= height[i]) {
            p = lessFromRight[p];
        }
        lessFromRight[i] = p;
    }

    int maxArea = 0;
    for (int i = 0; i < height.size(); i++) {
        maxArea = max(maxArea, height[i] * (lessFromRight[i] - lessFromLeft[i] - 1));
    }

    return maxArea;
    }
};