30 Day Challenge Day 15 | Leetcode 329. Longest Increasing Path in a Matrix

题解

Hard

方法一：DFS + Memoization

class Solution {
public:
    int longestIncreasingPath(vector<vector<int>>& matrix) {
        if(matrix.empty()) return 0;

        m = matrix.size(), n = matrix[0].size();
        
        vector<vector<int>> cache(m, vector<int>(n, 0));
        
        int res = 1;
        
        for(int i = 0; i < m; i++) {
            for(int j = 0; j < n; j++) {
                res = max(res, dfs(matrix, i, j, cache));
            }
        }
        
        return res;
    }
    
    int dfs(vector<vector<int>>& matrix, int x, int y, vector<vector<int>>& cache) {
        if(cache[x][y] != 0) return cache[x][y];
        
        cache[x][y] = 1;

        for(int i = 0; i < 4; i++) {
            int new_x = x + dirs[i][0];
            int new_y = y + dirs[i][1];
            if(new_x >= 0 && new_x < m && new_y >= 0 && new_y < n
              && matrix[new_x][new_y] > matrix[x][y]) {
                cache[x][y] = max(cache[x][y], dfs(matrix, new_x, new_y, cache) + 1);
            }
        }
        
        return cache[x][y];
    }
    
private:
    int dirs[4][2] = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};
    int m, n;
};