【DFS 或 BFS 或拓扑排序 - LeetCode】329. 矩阵中的最长递增路径

class Solution {
public:
    static constexpr int d[4][2] = {{-1,0},{1,0},{0,-1},{0,1}};
    int rows, cols;
    int dfs(vector<vector<int>>&matrix, int row, int col, vector<vector<int>>&dist){
        // 已经搜索过
        if(dist[row][col] != 0){
            return dist[row][col];
        }
        dist[row][col] ++;
        for(int i = 0; i < 4; i ++){
            int x = row + d[i][0];
            int y = col + d[i][1];
            if(x >= 0 && x < rows && y>= 0 && y < cols && matrix[x][y] > matrix[row][col]){
                // 记忆化搜索，并存储符合条件情况
                dist[row][col] = max(dist[row][col], dfs(matrix,x,y,dist)+1);
            }
        }
        return dist[row][col];
    }

    int longestIncreasingPath(vector<vector<int>>& matrix) {
        if(matrix.size() == 0 || matrix[0].size() == 0){
            return 0;
        }
        rows = matrix.size();
        cols = matrix[0].size();
        auto dist = vector<vector<int>>(rows, vector<int>(cols));
        int ans = 0;
        for(int i = 0; i < rows; i ++){
            for(int j = 0; j < cols; j ++){
                // 依次对每一个点进行dfs
                ans = max(ans, dfs(matrix,i,j,dist)); 
            }
        }
        return ans;
    }
};