main.py

class Solution(object):
    def intervalIntersection(self, firstList, secondList):
        """
        :type firstList: List[List[int]]
        :type secondList: List[List[int]]
        :rtype: List[List[int]]
        """
        i = 0
        j = 0
      
        result = []
        while i < len(firstList) and j < len(secondList):
            a_start, a_end = firstList[i]
            b_start, b_end = secondList[j]
            if a_start <= b_end and b_start <= a_end:                       # Criss-cross lock
                result.append([max(a_start, b_start), min(a_end, b_end)])   # Squeezing

            if a_end <= b_end:         # Exhausted this range in A
                i += 1               # Point to next range in A
            else:                      # Exhausted this range in B
                j += 1               # Point to next range in B
        return result