day 10

Author: sachuverma

Leetcode Daily Challenge/April-2021/10. Longest Increasing Path in a Matrix.cpp

@@ -0,0 +1,70 @@
+/*
+Longest Increasing Path in a Matrix
+===================================
+
+Given an m x n integers matrix, return the length of the longest increasing path in matrix.
+
+From each cell, you can either move in four directions: left, right, up, or down. You may not move diagonally or move outside the boundary (i.e., wrap-around is not allowed).
+
+Example 1:
+Input: matrix = [[9,9,4],[6,6,8],[2,1,1]]
+Output: 4
+Explanation: The longest increasing path is [1, 2, 6, 9].
+
+Example 2:
+Input: matrix = [[3,4,5],[3,2,6],[2,2,1]]
+Output: 4
+Explanation: The longest increasing path is [3, 4, 5, 6]. Moving diagonally is not allowed.
+
+Example 3:
+Input: matrix = [[1]]
+Output: 1
+
+Constraints:
+m == matrix.length
+n == matrix[i].length
+1 <= m, n <= 200
+0 <= matrix[i][j] <= 231 - 1
+*/
+
+class Solution
+{
+public:
+  int dirs[4][4] = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};
+
+  int dfs(vector<vector<int>> &mat, int r, int c, vector<vector<int>> &memo)
+  {
+    if (memo[r][c] != -1)
+      return memo[r][c];
+
+    int n = mat.size(), m = mat[0].size();
+    int ans = 0;
+    for (auto &dir : dirs)
+    {
+      int nextR = r + dir[0], nextC = c + dir[1];
+      if (nextR < 0 || nextC < 0 || nextR >= n || nextC >= m || mat[r][c] >= mat[nextR][nextC])
+        continue;
+      ans = max(ans, dfs(mat, nextR, nextC, memo));
+    }
+
+    memo[r][c] = ans + 1;
+    return memo[r][c];
+  }
+
+  int longestIncreasingPath(vector<vector<int>> &matrix)
+  {
+    int n = matrix.size(), m = matrix[0].size();
+    vector<vector<int>> memo(n + 1, vector<int>(m + 1, -1));
+
+    int ans = 0;
+    for (int i = 0; i < n; ++i)
+    {
+      for (int j = 0; j < m; ++j)
+      {
+        int curr_ans = dfs(matrix, i, j, memo);
+        ans = max(ans, curr_ans);
+      }
+    }
+    return ans;
+  }
+};

Leetcode Daily Challenge/April-2021/README.md

@@ -11,3 +11,4 @@
 | 7.  | [Determine if String Halves Are Alike](https://leetcode.com/explore/challenge/card/april-leetcoding-challenge-2021/593/week-1-april-1st-april-7th/3699/)   |  [cpp](./07.%20Determine%20if%20String%20Halves%20Are%20Alike.cpp)  |
 | 8.  | [Letter Combinations of a Phone Number](https://leetcode.com/explore/challenge/card/april-leetcoding-challenge-2021/594/week-2-april-8th-april-14th/3701/)   |  [cpp](./08.%20Letter%20Combinations%20of%20a%20Phone%20Number.cpp)  |
 | 9.  | [Verifying an Alien Dictionary](https://leetcode.com/explore/challenge/card/april-leetcoding-challenge-2021/594/week-2-april-8th-april-14th/3702/)   |  [cpp](./09.%20Verifying%20an%20Alien%20Dictionary.cpp)  |
+| 10.  | [Longest Increasing Path in a Matrix](https://leetcode.com/explore/challenge/card/april-leetcoding-challenge-2021/594/week-2-april-8th-april-14th/3703/)   |  [cpp](./10.%20Longest%20Increasing%20Path%20in%20a%20Matrix.cpp)  |