Find Right Interval — LeetCode 436 Python Solution

The problem

You are given an array of intervals, where intervals[i] = [starti, endi] and each starti is unique. The right interval for an interval i is an interval j such that startj >= endi and startj is minimized.

Example

Input

intervals = [[1,2]]

Output

[-1]

Explanation

There is only one interval in the collection, so it outputs -1.

Python solution

class Solution:
    def findRightInterval(self, intervals: List[List[int]]) -> List[int]:
        n = len(intervals)
        ans = [-1] * n
        arr = sorted((st, i) for i, (st, _) in enumerate(intervals))
        for i, (_, ed) in enumerate(intervals):
            j = bisect_left(arr, (ed, -inf))
            if j < n:
                ans[i] = arr[j][1]
        return ans

Complexity

Pattern: Monotonic Stack

Answer "what is the next greater element" for every position in one pass. LeetCode 436. Find Right Interval is filed here because the reference solution below belongs to the algorithm family this hub collects, even though its LeetCode tags point elsewhere.

The monotonic stack guide has the Python template for the pattern and the 225 LeetCode problems that use it.

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