leetcode 986. Interval List Intersections（python）

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描述

You are given two lists of closed intervals, firstList and secondList, where firstList[i] = [start_i, end_i] and secondList[j] = [start_j, end_j]. 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]]
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Example 2:

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

Input: firstList = [], secondList = [[4,8],[10,12]]
Output: []
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Example 4:

Input: firstList = [[1,7]], secondList = [[3,10]]
Output: [[3,7]]
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Note:

0 <= firstList.length, secondList.length <= 1000
firstList.length + secondList.length >= 1
0 <= start_i < end_i <= 109
end_i < start_i+1
0 <= start_j < end_j <= 109
end_j < start_j+1

解析

根据题意，给定两个闭区间列表，firstList 和 secondList，其中 firstList[i] = [start_i, end_i] 和 secondList[j] = [start_j, end_j]。每个区间列表都是成对不相交的，并按排序顺序排列。题目要求我们返回这两个区间列表的交集。

题目中还给出了闭区间和交集的概念，闭区间 [a, b]（a <= b）表示实数 x 的集合，a <= x <= b。两个闭区间的交集是一组实数，它们要么为空，要么表示为闭区间。例如，[1, 3] 和 [2, 4] 的交集是 [2, 3]。

思路很简单，直接遍历所有的闭区间找交集即可：

如果 A 或者 B 有一个为空列表，直接返回空列表
初始化两个指针 i 和 j 都为 0 ，结果 result 为空列表

当 i 小于 A 的长度并且 j 小于 B 的长度时候一直进行 while 循环

  如果 A[i][1] < B[j][0] 说明 A[i] 和 B[j] 没有交集，i 加一进行下一次循环
  同理 B[j][1] < A[i][0] 也说明  A[i] 和 B[j] 没有交集 ，j 加一进行下一次循环
  如果有交集，直接将其存入 result 中
  如果 A[i][1] < B[j][1] 说明需要查看 A[i+1] 与 B[j] 是否存在交集，所以  i 加一，否则 j 加一，一样的道理
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循环结束返回 result 即可。

解答

class Solution(object):
    def intervalIntersection(self, A, B):
        """
        :type A: List[List[int]]
        :type B: List[List[int]]
        :rtype: List[List[int]]
        """
        if not A or not B: return []
        i = j = 0
        result = []
        while i < len(A) and j < len(B):
            if A[i][1] < B[j][0]:
                i += 1
                continue
            if B[j][1] < A[i][0]:
                j += 1
                continue
            result.append([max(A[i][0], B[j][0]), min(A[i][1], B[j][1])])
            if A[i][1] < B[j][1]:
                i += 1
            else:
                j += 1
        return result
        	      
		
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运行结果

Runtime: 116 ms, faster than 90.07% of Python online submissions for Interval List Intersections.
Memory Usage: 14.3 MB, less than 69.98% of Python online submissions for Interval List Intersections.	
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解析

还可以有简化一下代码，原理同上。

解答

class Solution(object):
    def intervalIntersection(self, A, B):
        """
        :type A: List[List[int]]
        :type B: List[List[int]]
        :rtype: List[List[int]]
        """
        if not A or not B: return []
        i = j = 0
        result = []
        while i < len(A) and j < len(B):
            L = max(A[i][0], B[j][0])
            R = min(A[i][1], B[j][1])
            if L<=R:
                result.append([L, R])
            if A[i][1] < B[j][1]:
                i += 1
            else:
                j += 1
        return result
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运行结果

Runtime: 112 ms, faster than 96.69% of Python online submissions for Interval List Intersections.
Memory Usage: 14.3 MB, less than 69.98% of Python online submissions for Interval List Intersections.
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原题链接：leetcode.com/problems/in…

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