【leetcode】986. Interval List Intersections (双指针)
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]]
这道题需要求两个数组的公共区间的集合,如果用暴力法的话时间复杂度就是o(mn),如果用双指针的话时间复杂度就是o(m+n),这道题用双指针很有意思,需要注意的是两个指针的更新规则。
class Solution { public: vector<vector<int>> intervalIntersection(vector<vector<int>>& firstList, vector<vector<int>>& secondList) { // 暴力法的时间复杂就是o(mn) // 利用双指针检索 时间复杂度为o(m+n) 用i j 分别指向firstlist 以及secondlist 中的元素 vector<vector<int>> res; int m=firstList.size(),n=secondList.size(); int i=0,j=0; //双指针 while(i<m && j<n){ if(firstList[i][1]<secondList[j][0]) i++; else if(firstList[i][0]>secondList[j][1]) j++; //没有交集 小的区间向后移动 else{ res.push_back({max(firstList[i][0],secondList[j][0]),min(firstList[i][1],secondList[j][1])}); //存储交集区间 if(firstList[i][1]<secondList[j][1]) i++; else if (firstList[i][1]>secondList[j][1]) j++; else{ i++; j++; } } } return res; } };