778. Swim_in_Rising_Water

class Solution {
public:        
    int swimInWater(vector<vector<int>>& grid) {
        
        int n=grid.size(),ans=0;
        priority_queue<vector<int>,vector<vector<int>>,greater<vector<int>>> q;
        unordered_map<int,bool> visited;
        vector<int> d={1,0,-1,0,1};
        
        q.push({grid[0][0],0,0});
        visited[0]=true;
        
        while(!q.empty())
        {
            auto p=q.top();
            q.pop();
            // ans=max(ans,p[0]);
            for(int i=0;i<4;i++)
            {
                int X=p[1]+d[i];
                int Y=p[2]+d[i+1];
                if(X>=0&&Y>=0&&X<n&&Y<n)
                {
                    if(X==n-1&&Y==n-1)
                        return max(p[0],grid[n-1][n-1]);
                    if(!visited[X*n+Y]){
                        q.push({max(grid[X][Y],p[0]),X,Y});
                        visited[X*n+Y]=true;
                    }
                }
            }
        }
      return 0;  
    }
};