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Program to find largest rectangle area under histogram in python
Suppose we have a list of numbers representing heights of bars in a histogram. We have to find area of the largest rectangle that can be formed under the bars.
So, if the input is like nums = [3, 2, 5, 7]
then the output will be 10
To solve this, we will follow these steps −
- stk := a stack and initially insert -1 into it
- insert 0 at the end of heights
- ans := 0
- for i in range 0 to size of heights, do
- while heights[i] < heights[top of stk], do
- h := heights[top of stk] and pop from stk
- w := i - top of stk - 1
- ans := maximum of ans and (h * w)
- push i into stk
- while heights[i] < heights[top of stk], do
- return ans
Let us see the following implementation to get better understanding −
Example
class Solution: def solve(self, heights): stk = [-1] heights.append(0) ans = 0 for i in range(len(heights)): while heights[i] < heights[stk[-1]]: h = heights[stk.pop()] w = i - stk[-1] - 1 ans = max(ans, h * w) stk.append(i) return ans ob = Solution() nums = [3, 2, 5, 7] print(ob.solve(nums))
Input
[3, 2, 5, 7]
Output
10
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