leetcode： Memoization：Longest Increasing Path in a Matrix（329）

class Solution {
public:
bool checkRange(vector<vector<int> >& matrix, int x, int y) {
int n = matrix.size(), m = matrix[0].size();
if(x < 0 || y < 0 || x >= n || y >= m)  return false;
return true;
}

int dfs(vector<vector<int> >& matrix, vector<vector<int> >& dp, vector<vector<bool> >& vis, vector<vector<int> >& dir, int x, int y) {
if(dp[x][y])  return dp[x][y];

int MAX = -1;
for(int i=0; i<dir.size(); ++i) {
int nx = x + dir[i][0], ny = y + dir[i][1];
if(checkRange(matrix, nx, ny) && !vis[nx][ny] && matrix[nx][ny] > matrix[x][y]) {
vis[nx][ny] = true;
MAX = max(MAX, dfs(matrix, dp, vis, dir, nx, ny) + 1);
vis[nx][ny] = false;
}
}

if(MAX == -1) return 1;
dp[x][y] = MAX;
return dp[x][y];
}

int longestIncreasingPath(vector<vector<int>>& matrix) {
int n = matrix.size();
if(n == 0)  return 0;

int m = matrix[0].size();
vector<vector<int> > dp(n, vector<int>(m, 0));
vector<vector<bool> > vis(n, vector<bool>(m, false));
vector<vector<int> > dir(4);
dir[0].push_back(-1);  dir[0].push_back(0);
dir[1].push_back(0);  dir[1].push_back(1);
dir[2].push_back(1);  dir[2].push_back(0);
dir[3].push_back(0);  dir[3].push_back(-1);

int res = -1;
for(int i=0; i<n; ++i) {
for(int j=0; j<m; ++j) {
vis[i][j] = true;
dp[i][j] = dfs(matrix, dp, vis, dir, i, j);
res = max(res, dp[i][j]);
vis[i][j] = false;
}
}

return res;
}
};