1254.Number_of_Closed_Islands.cpp

/*
    written by Pankaj Kumar.
    country:-INDIA
*/
typedef long long ll ;
typedef vector<int> vl;
typedef vector<vector<int>> vvl;
#define speed cin.tie(0);cout.tie(0);ios_base::sync_with_stdio(0);
/*  Abbrevations  */
#define ff first
#define ss second
#define mp make_pair
#define pb push_back
// Some print
#define no cout<<"NO"<<endl;
#define yes cout<<"YES"<<endl;
// sort
#define all(V) (V).begin(),(V).end()
#define srt(V) sort(all(V))
#define srtGreat(V) sort(all(V),greater<ll>())
// some extra
#define printv(v) for(ll i=0;i<ll(v.size());i++){cout<<v[i]<<" ";} cout<<endl;
#define precision(x) cout<<fixed<<setprecision(x);
#define sz(V) ll(V.size())


/* ascii value
A=65,Z=90,a=97,z=122
*/

/* Some syntax 
//Syntax to create a min heap for priority queue
//priority_queue <int, vector<int>, greater<int>>pq;
*/
/*  --------------------MAIN PROGRAM----------------------------*/
// to run ctrl+b
const ll INF=1e18;
const ll mod1=1e9+7;
const ll mod2=998244353;
// Techniques :
// divide into cases, brute force, pattern finding
// sort, greedy, binary search, two pointer
// transform into graph

// Experience :
// Cp is nothing but only observation and mathematics.


//Add main code here

class Solution {
public:
    int closed_islands=0;
    vector<vector<bool>> check;

    void dfs(vector<vector<int>>& grid,int i,int j,bool& flag){
        if(i<0 || j<0 || i>=ll(grid.size()) || j>=ll(grid[0].size()) || grid[i][j]==1 || check[i][j]){
            return;
        }
        check[i][j]=true;
        if(i==0 || j==0 || i==ll(grid.size())-1 || j==ll(grid[0].size())-1){
            flag=false;
        }
        dfs(grid,i+1,j,flag);
        dfs(grid,i-1,j,flag);
        dfs(grid,i,j+1,flag);
        dfs(grid,i,j-1,flag);
    }

    int closedIsland(vector<vector<int>>& grid) {
        int n=sz(grid);
        int m=sz(grid[0]);
        check.resize(n,vector<bool>(m,false));
        for(int i=0;i<n;i++){
            for(int j=0;j<m;j++){
                if(grid[i][j]==0 && check[i][j]==false){
                    bool flag=true;
                    dfs(grid,i,j,flag);
                    if(flag){
                        closed_islands++;
                    }
                }
            }
        }
        return closed_islands;
    }
};


/* -----------------END OF PROGRAM --------------------*/
/*
* stuff you should look before submission
* constraint and time limit
* int overflow
* special test case (n=0||n=1||n=2)
* don't get stuck on one approach if you get wrong answer
*/