1020. Number of Enclaves

Link

Solution

DFS all edges first to let the node connecting to the edge become 0.

Then check how many node[i][j] left, which node[i][j] == 1

    public int numEnclaves(int[][] A) {
        int M = A.length;
        int N = A[0].length;
        for(int i = 0; i < M; i++){
            for(int j = 0; j < N; j++){
                if(i == 0 || j == 0 || i == M-1 || j == N-1){
                    dfs(A, i, j);
                }
            }
        }
        
        int count = 0;
        for(int i = 0; i < M; i++){
            for(int j = 0; j < N; j++){
                if(A[i][j] == 1)
                    count++;
                
            }
        }
        return count;
      
    }
    
    public void dfs(int[][] A, int i, int j){
        int M = A.length;
        int N = A[0].length;
        if(i < 0 || i >= M || j < 0 || j >= N || A[i][j] == 0) return;
        A[i][j] = 0;
        int[][] dirs = new int[][]{{0,1}, {1,0}, {0,-1}, {-1,0}};
        
        for(int[] dir : dirs){
            dfs(A, i+dir[0], j+dir[1]);
        }
    }