Leetcode: largest rectangle in Histogram

Leetcode: largest rectangle in Histogram

GivenNNon-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 =10Unit.

For example,
Given Height =[2,1,5,6,2,3],
Return10.

Address: https://oj.leetcode.com/problems/largest-rectangle-in-histogram/

Algorithm: calculate the maximum rectangular area with the height of each bar as the width. The largest area is the largest area. You can find the subscript of the first bar lower than this bar on the left, as left_index, right find the subscript of the first bar lower than this bar, as right_index, the bar corresponds to the rectangular area = H [I] * (right_index-left_index ). The stack can be used to calculate the time complexity to O (n ). First, the condition for Stack entry is that the height of the empty stack or bar currently traversed is higher than that of the top of the stack. If the appeal condition is not met, the stack is released. This ensures that the node currently traversed must be the left_index of the stack element, and the next node of the stack element is right_index. Code:

 1 class Solution { 2 public: 3     int largestRectangleArea(vector<int> &height) { 4         int len = height.size(); 5         if(len < 1) return 0; 6         stack<int> stk; 7         int i = 0; 8         int max_area = 0; 9         while(i < len){10             if(stk.empty() || height[stk.top()] <= height[i]){11                 stk.push(i++);12             }else{13                 int t = stk.top();14                 stk.pop();15                 int area = height[t] * (stk.empty() ? i : i - stk.top() - 1);16                 if(area > max_area){17                     max_area = area;18                 }19             }20         }21         while(!stk.empty()){22             int t = stk.top();23             stk.pop();24             int area = height[t] * (stk.empty() ? len : len - stk.top() - 1);25             if(area > max_area){26                 max_area = area;27             }28         }29         return max_area;30     }31 };

 

Leetcode: largest rectangle in Histogram