class Solution:
    def intervalIntersection(self, firstList: List[List[int]], secondList: List[List[int]]) -> List[List[int]]:
        flp, slp = 0,0
        overlaps = []
        while flp < len(firstList) and slp < len(secondList):
            m1 = firstList[flp]
            m2 = secondList[slp]

            overlap = [max(m1[0], m2[0]), min(m1[1], m2[1])]
            
            if overlap[0] <= overlap[1]:
                # found valid overlap
                overlaps.append(overlap)
            
            if m1[1] <= m2[1]:
                flp+=1
            else:
                slp+=1
        
        return overlaps