329

Author: lzl124631x

leetcode/329. Longest Increasing Path in a Matrix/README.md

@@ -27,6 +27,7 @@ Return `4`
 The longest increasing path is `[3, 4, 5, 6]`. Moving diagonally is not allowed.
 
 # Solution 1. DFS
+
 Typical DFS. Use a `vector<vector<int>> cnt`, where `cnt[i][j]` is the length of longest increasing path starting from `matrix[i][j]`. Initially values in `cnt` are all zeroes.
 
 For each position `matrix[x][y]`,
@@ -64,4 +65,51 @@ public:
     return ans;
   }
 };
+```
+
+## Solution 2. Topological Sort
+
+```cpp
+// OJ: https://leetcode.com/problems/longest-increasing-path-in-a-matrix/
+// Author: github.com/lzl124631x
+// Time: O(MN)
+// Space: O(MN)
+// Ref: https://leetcode.com/problems/longest-increasing-path-in-a-matrix/discuss/288520/BFS-Implemented-Topological-Sort
+class Solution {
+public:
+    int longestIncreasingPath(vector<vector<int>>& A) {
+        if (A.empty() || A[0].empty()) return 0;
+        int M = A.size(), N = A[0].size(), ans = 0, dirs[4][2] = {{0,1},{0,-1},{1,0},{-1,0}};
+        vector<vector<int>> indegree(M, vector<int>(N));
+        for (int i = 0; i < M; ++i) {
+            for (int j = 0; j < N; ++j) {
+                for (auto &dir : dirs) {
+                    int x = i + dir[0], y = j + dir[1];
+                    if (x < 0 || x >= M || y < 0 || y >= N || A[x][y] <= A[i][j]) continue;
+                    indegree[x][y]++;
+                }
+            }
+        }
+        queue<vector<int>> q;
+        for (int i = 0; i < M; ++i) {
+            for (int j = 0; j < N; ++j) {
+                if (indegree[i][j] == 0) q.push({ i, j });
+            }
+        }
+        while (q.size()) {
+            int sz = q.size();
+            while (sz--) {
+                int x = q.front()[0], y = q.front()[1];
+                q.pop();
+                for (auto &dir : dirs) {
+                    int a = x + dir[0], b = y + dir[1];
+                    if (a < 0 || a >= M || b < 0 || b >= N || A[a][b] <= A[x][y]) continue;
+                    if (--indegree[a][b] == 0) q.push({ a, b });
+                }
+            }
+            ++ans;
+        }
+        return ans;
+    }
+};
 ```

leetcode/329. Longest Increasing Path in a Matrix/s2.cpp

@@ -0,0 +1,42 @@
+// OJ: https://leetcode.com/problems/longest-increasing-path-in-a-matrix/
+// Author: github.com/lzl124631x
+// Time: O(MN)
+// Space: O(MN)
+// Ref: https://leetcode.com/problems/longest-increasing-path-in-a-matrix/discuss/288520/BFS-Implemented-Topological-Sort
+class Solution {
+public:
+    int longestIncreasingPath(vector<vector<int>>& A) {
+        if (A.empty() || A[0].empty()) return 0;
+        int M = A.size(), N = A[0].size(), ans = 0, dirs[4][2] = {{0,1},{0,-1},{1,0},{-1,0}};
+        vector<vector<int>> indegree(M, vector<int>(N));
+        for (int i = 0; i < M; ++i) {
+            for (int j = 0; j < N; ++j) {
+                for (auto &dir : dirs) {
+                    int x = i + dir[0], y = j + dir[1];
+                    if (x < 0 || x >= M || y < 0 || y >= N || A[x][y] <= A[i][j]) continue;
+                    indegree[x][y]++;
+                }
+            }
+        }
+        queue<vector<int>> q;
+        for (int i = 0; i < M; ++i) {
+            for (int j = 0; j < N; ++j) {
+                if (indegree[i][j] == 0) q.push({ i, j });
+            }
+        }
+        while (q.size()) {
+            int sz = q.size();
+            while (sz--) {
+                int x = q.front()[0], y = q.front()[1];
+                q.pop();
+                for (auto &dir : dirs) {
+                    int a = x + dir[0], b = y + dir[1];
+                    if (a < 0 || a >= M || b < 0 || b >= N || A[a][b] <= A[x][y]) continue;
+                    if (--indegree[a][b] == 0) q.push({ a, b });
+                }
+            }
+            ++ans;
+        }
+        return ans;
+    }
+};