Li Kou 986. Intersection of interval lists

Power button 986. Intersection of interval list （ Review by yourself ）
Consider the minimum end point , For example 1 in , The minimum end point is A[0], So because the intervals in the two lists do not intersect ,A[0] Only possible with B An interval in B[0] The intersection （ otherwise B The central district will intersect ）, that A[0] It is impossible to intersect with other intervals in the future , You can no longer consider （ delete ）, At this point, we need to find the next minimum end point , To continue the appeal process .
Why is the next minimum end point not B[0] Well , Because there may be the following ：

So the code is as follows ：

class Solution:
    def intervalIntersection(self, firstList: List[List[int]], secondList: List[List[int]]) -> List[List[int]]:
        ret=[]
        i=j=0	# The double pointer points to the current comparison interval 
        while i<len(firstList) and j<len(secondList):
            # Find intersection interval 
            start=max(firstList[i][0],secondList[j][0])
            end=min(firstList[i][1],secondList[j][1])
            
            if start<=end:
                ret.append([start,end])
                
            # Find the interval where the minimum end point exists  
            if firstList[i][1]<secondList[j][1]:
                i+=1
            else:
                j+=1
        return ret