[
[1,1,0,0,0],
[0,1,0,1,1],
[0,0,0,1,1],
[0,0,0,0,0],
[0,0,1,1,1]
]

public class Solution {
    /**
     * 判斷島嶼數(shù)量
     * @param grid char字符型二維數(shù)組
     * @return int整型
     */
    public int solve (char[][] grid) {
        int total = 0;
        if(grid.length == 0 || grid[0].length == 0){
            return total;
        }
        int wl = grid[0].length;
        for(int i=0; i < grid.length; i++){
            for(int j =0; j < wl; j++){
                if(grid[i][j] == '1'){
                    total++;
                    cancel(grid, i, j);
                }
            }
        }
        return total;
    }
    private void cancel(char[][] grid, int i, int j){
        if(grid[i][j] == '1'){
            grid[i][j] = '0';
            if(i > 0){
                cancel(grid, i-1, j);
            }
            if(j > 0){
                cancel(grid, i, j-1);
            }
            if(j < grid[0].length -1){
                cancel(grid, i, j+1);
            }
            if(i < grid.length - 1){
                cancel(grid, i+1, j);
            }
        }
    }
}

public class Student {
    public int sex; // 男是1
}

List<Student> students = new getAllStudents();
for (int i = 0; i < students.size(); i++) {
    if (students.get(i).sex == 1){
        students.remove(students.get(i));
    }
}

List<Student> students = new getAllStudents();
List<Student> girls = new ArrayList<>();
for (int i = 0; i < students.size(); i++) {
    if (students.get(i).sex == 0){
        girls.add(students.get(i));
    }
}
students = girls;