user2914144 - 1 month ago 7
Python Question

# Receiving a KeyError: '0_0' for my python program

I'm was working on this question (it's from Leetcode):

"Given an integer matrix, find the length of the longest increasing
path.

From each cell, you can either move to four directions: left, right, up or down.
You may NOT move diagonally or move outside of the
boundary (i.e. wrap-around is not allowed).

``````Example 1:

nums = [
[9,9,4],
[6,6,8],
[2,1,1]
]
Return 4.
``````

I keep running into a KeyError specifically:

``````Traceback (most recent call last):
File "/Users/Desktop/longest_increasing_path_in_a_matrix.py", line 41, in <module>
print(test.longestIncreasingPath(matrix))
File "/Users/Desktop/longest_increasing_path_in_a_matrix.py", line 31, in longestIncreasingPath
traverse(x, y, [])
File "/Users/Desktop/longest_increasing_path_in_a_matrix.py", line 5, in traverse
if traverse.traveled[str(x_coor) + "_" + str(y_coor)]:
KeyError: '0_0'
``````

and I'm not sure exactly what I'm doing wrong. I understand it has to do with my dictionary. Please let me know if there is anything else I need to post:

``````class Solution(object):
def longestIncreasingPath(self, matrix):

def traverse(x_coor, y_coor, build):
key = str(x_coor) + "_" + str(y_coor)
if key in traverse.traveled and traverse.traveled[key]:
if traveled[str(x_coor) + "_" + str(y_coor)]:
return
elif x_coor < 0 or y_coor < 0 or x_coor >= len(matrix[0]) or y_coor >= len(matrix)-1:
return
elif len(build) > 0 and matrix[x_coor][y_coor] <= build[-1]:
if len(build) > traverse.count:
traverse.count = len(build)
return

traveled[str(x_coor) + "_" + str(y_coor)] = true
build.append(matrix[y_coor][x_coor])
traverse(x_coor, y_coor-1, build)
traverse(x_coor, y_coor+1, build)
traverse(x_coor+1, y_coor, build)
traverse(x_coor-1, y_coor, build)
build.pop()
del traveled[str(x_coor) + "_" + str(y_coor)]

traverse.count = 0
traverse.traveled = {}

for y in range(0, len(matrix)-1, 1):
for x in range(0, len(matrix[0]), 1):
traverse(x, y, [])

return(traverse.count)
matrix = [
[9,9,4],
[6,6,8],
[2,1,1]
]
test = Solution()
print(test.longestIncreasingPath(matrix))
``````

You are trying to access a key (`0_0`) that doesn't exist yet in the dictionary.
You have to check beforehand if it exists, I'd suggest the `in` keyword:
``````key = str(x_coor) + "_" + str(y_coor)