986. Interval List Intersections

双指针 区间

You are given two lists of closed intervals, firstList and secondList, where firstList[i] = [starti, endi] and secondList[j] = [startj, endj]. Each list of intervals is pairwise disjoint and in sorted order.

Return the intersection of these two interval lists.

A closed interval [a, b] (with a <= b) denotes the set of real numbers x with a <= x <= b.

The intersection of two closed intervals is a set of real numbers that are either empty or represented as a closed interval. For example, the intersection of [1, 3] and [2, 4] is [2, 3].

Example 1:

Input: firstList = [[0,2],[5,10],[13,23],[24,25]], secondList = [[1,5],[8,12],[15,24],[25,26]]
Output: [[1,2],[5,5],[8,10],[15,23],[24,24],[25,25]]

Example 2:

Input: firstList = [[1,3],[5,9]], secondList = []
Output: []

Constraints:

• 0 <= firstList.length, secondList.length <= 1000

• firstList.length + secondList.length >= 1

• 0 <= starti < endi <= 109

• endi < starti+1

• 0 <= startj < endj <= 109

• endj < startj+1

分析

双指针指向两区间，移动结束时间更早的指针。

class Solution:
    def intervalIntersection(self, firstList: List[List[int]], secondList: List[List[int]]) -> List[List[int]]:
        i = j = 0
        res = []
        while i < len(firstList) and j < len(secondList):
            s1, e1 = firstList[i]
            s2, e2 = secondList[j]
            start = max(s1,s2)
            end = min(e1,e2)
            if start <= end:
                res.append([start, end])
            if e1 < e2:
                i += 1
            else:
                j += 1
        return res