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leetcode 986. Interval List Intersections(python)

2022-01-31 19:01:55 Wang Daya

「 This is my participation 11 The fourth of the yuegengwen challenge 18 God , Check out the activity details :2021 One last more challenge

describe

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]]
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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 <= starti < endi <= 109
  • endi < starti+1
  • 0 <= startj < endj <= 109
  • endj < startj+1

analysis

According to the meaning , Given two closed interval lists ,firstList and secondList, among firstList[i] = [starti, endi] and secondList[j] = [startj, endj]. Each interval list is disjoint in pairs , And sort them in order . The title asks us to return the intersection of these two interval lists .

The concepts of closed interval and intersection are also given in the title , Closed interval [a, b](a <= b) For real numbers x Set ,a <= x <= b. The intersection of two closed intervals is a set of real numbers , They are either empty , Or expressed as a closed interval . for example ,[1, 3] and [2, 4] The intersection of [2, 3].

The idea is simple , Directly traverse all closed intervals to find the intersection :

  • If A perhaps B There is an empty list , Return the empty list directly

  • Initialize two pointers i and j All for 0 , result result Empty list

  • When i Less than A And j Less than B The length of time has been carried out while loop

       If  A[i][1] < B[j][0]  explain  A[i]  and  B[j]  There is no intersection ,i  Add one for the next cycle 
       Empathy  B[j][1] < A[i][0]  Also explain   A[i]  and  B[j]  There is no intersection  ,j  Add one for the next cycle 
       If there is an intersection , Deposit it directly into  result  in 
       If  A[i][1] < B[j][1]  Description needs to be viewed  A[i+1]  And  B[j]  Whether there is an intersection , therefore   i  Add one , otherwise  j  Add one , The same thing 
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  • Return to the end of the loop result that will do .

answer

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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Running results

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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analysis

You can also simplify the code , The principle of same .

answer

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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Running results

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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Original link :leetcode.com/problems/in…

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author[Wang Daya],Please bring the original link to reprint, thank you.
https://en.pythonmana.com/2022/01/202201311901537512.html

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