1n73r\/4L

class Solution:
    def intervalIntersection(self, A: List[List[int]], B: List[List[int]]) -> List[List[int]]:
        ans = []
        i, j = 0, 0 # look at two intervals at a time, A[i] and B[j]
        while i < len(A) and j < len(B):
            # find bounds of intersection (if two intervals intersect)
            lower = max(A[i][0], B[j][0])
            higher = min(A[i][1], B[j][1])

            if lower <= higher:
                # is an intersection; add to answer
                ans += [[lower, higher]]

            # now look at a different pair of intervals
            if A[i][1] < B[j][1]: # A[i] ended before B[j]
                i += 1
            elif A[i][1] > B[j][1]: # B[j] ended before A[i]
                j += 1
            else: # note if both intervals end at the same time, both i and j increments
                i += 1
                j += 1
        return ans