Leetcode 498. Diagonal Traverse

Seawolf

1. Given a matrix of M x N elements (M rows, N columns), return all elements of the matrix in diagonal order as shown in the below image.
   
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5. Example:
   
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7. Input:
   
8. [
   
9. [ 1, 2, 3 ],
   
10. [ 4, 5, 6 ],
    
11. [ 7, 8, 9 ]
    
12. ]
    
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14. Output:  [1,2,4,7,5,3,6,8,9]
    
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16. Explanation:
    
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20. Note:
    
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22. The total number of elements of the given matrix will not exceed 10,000.

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1. class Solution:
   
2.     def findDiagonalOrder(self, matrix: List[List[int]]) -> List[int]:
   
3.         result = []
   
4.         if matrix == None or len(matrix) == 0 or len(matrix[0]) == 0:
   
5.             return result
   
6.         m = len(matrix)
   
7.         n = len(matrix[0])
   
8.         hashmap = collections.defaultdict(list)
   
9.         for i in range(m):
   
10.             for j in range(n):
    
11.                 hashmap[i + j].append(matrix[i][j])
    
12.         for k in sorted(hashmap.keys()):
    
13.             temp = hashmap[k]
    
14.             if k % 2 == 0:
    
15.                 temp = temp[::-1]
    
16.             result += temp
    
17.         return result

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