329. 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).

class Solution {
    int dp[200][200];
    int dx[4]{0,1,0,-1}, dy[4]{-1,0,1,0};
    int dfs(vector<vector<int>>& matrix, int& n, int& m, int y, int x) {
        if(dp[y][x] != -1) return dp[y][x];
        dp[y][x] = 1;
        for(int i = 0; i < 4; i++) {
            int ny = y + dy[i], nx = x + dx[i];
            if(0<=nx and nx < m and 0 <= ny and ny < n and matrix[ny][nx] > matrix[y][x]) {
                dp[y][x] = max(dp[y][x], dfs(matrix,n,m,ny,nx) + 1);
            }
        }
        return dp[y][x];
    }
public:
    int longestIncreasingPath(vector<vector<int>>& matrix) {
        memset(dp,-1,sizeof(dp));
        int n = matrix.size(), m = matrix[0].size(), res = 0;
        for(int i = 0; i < n; i++)
            for(int j = 0; j < m; j++)
                res = max(res, dfs(matrix, n, m, i, j));
    
        return res;
    }
};