542

Author: ProHiryu

DFS/traditionalDFS/542.md

@@ -0,0 +1,39 @@
+## 542 01 Matrix
+
+#### Description
+
+[link](https://leetcode.com/problems/01-matrix/)
+
+---
+
+#### Solution
+
+两遍循环的解法，对这种题目很有帮助
+
+---
+
+#### Code
+
+> O(n^2)
+
+```python
+class Solution:
+    def updateMatrix(self, matrix: List[List[int]]) -> List[List[int]]:
+        m, n = len(matrix), len(matrix and matrix[0])
+        for i in range(m):
+            for j in range(n):
+                if matrix[i][j] != 0:
+                    matrix[i][j] = float("inf")
+                    if i > 0 and matrix[i - 1][j] + 1 < matrix[i][j]:
+                        matrix[i][j] = matrix[i - 1][j] + 1
+                    if j > 0 and matrix[i][j - 1] + 1 < matrix[i][j]:
+                        matrix[i][j] = matrix[i][j - 1] + 1
+        for i in range(m - 1, -1, -1):
+            for j in range(n - 1, -1, -1):
+                if matrix[i][j] != 0:
+                    if i + 1 < m and matrix[i + 1][j] + 1 < matrix[i][j]:
+                        matrix[i][j] = matrix[i + 1][j] + 1
+                    if j + 1 < n and matrix[i][j + 1] + 1 < matrix[i][j]:
+                        matrix[i][j] = matrix[i][j + 1] + 1
+        return matrix
+```