class Solution:
    def findDiagonalOrder(self, nums: List[List[int]]) -> List[int]:
        arr = []
        l = len(nums)
        d = {}
        for i in range(l):
            for j in range(len(nums[i])):
                if(i+j not in list(d.keys())):
                    d[i+j] = []
                d[i+j].append(nums[i][j])

        for key in list(d.keys()):
            diag = d[key]
            l = len(diag)
            for i in range(l)[::-1]:
                arr.append(diag[i])
        return arr