1020. 飞地的数量.md

class Solution {
    private static final int[][] VECTOR = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}};
    public int numEnclaves(int[][] grid) {
        int len1 = grid.length - 1, len2 = grid[0].length - 1;
        for (int i = 0; i <= len1; i++) {
            numEnclavesDFS(grid, i, 0);
            numEnclavesDFS(grid, i, len2);
        }
        for (int i = 0; i <= len2; i++) {
            numEnclavesDFS(grid, 0, i);
            numEnclavesDFS(grid, len1, i);
        }
        int ans = 0;
        for (int[] is : grid)
            for (int i : is) if (i == 1) ans++;
        return ans;    
    }

    private void numEnclavesDFS(int[][] grid, int i, int j) {
        if (i < 0 || j < 0 || i == grid.length || j == grid[i].length || grid[i][j] == 0) return;
        grid[i][j] = 0;
        for (int[] is : VECTOR) numEnclavesDFS(grid, i + is[0], j + is[1]);
    }
}