# Find number of closed islands | Practice | GeeksforGeeks

Thu May 18 2023 19:36:49 GMT+0000 (Coordinated Universal Time)

Saved by @DxBros #dfs #closedislands

```class Solution {
public:
vector<int> dx{0, 1, -1, 0},dy{1, 0, 0, -1};
bool isVisitable(int x, int y, int N, int M){
return x>=0 && y>=0 && x<N && y<M;
}
void dfs(int i, int j, int N, int M, vector<vector<int>>& matrix){
for(int k =0 ; k <4; k++){
int x = i + dx[k], y = j + dy[k];
if( isVisitable(x, y, N, M) && matrix[x][y] != 0)
matrix[x][y]=0,dfs(x, y, N, M, matrix);
}
}
int closedIslands(vector<vector<int>>& matrix, int N, int M) {
// Code here
for(int i = 0; i < N; i++){
for(int j = 0; j < M ; j++){
if( (i == 0 || j == 0 || i == N -1 || j == M - 1 )&& matrix[i][j] == 1){
//check if 1 exists on the edges of matrix
//if yes visit all the cells that have 1 and are
//reachable from current cell and mark them visited by making 0
matrix[i][j] = 0;
dfs(i, j, N, M,matrix);
}
}
}

int ans = 0;
for(int i = 0 ; i < N; i++){
for(int j = 0; j < M ; j++){
if(matrix[i][j] == 1){
//whatever cells not visited in previous case
//we visit now and mark visited(0) and increment the