lintcode 443.岛屿的个数

public class Solution {
    
    /**
     * @param grid a boolean 2D matrix
     * @return an integer
     */
    public int numIslands(boolean[][] grid) {
        int res=0;
        for(int i=0;i<grid.length;i++){
            for(int j=0;j<grid[i].length;j++){
                if(grid[i][j]){
                    res++;
                    solve(grid,i,j);
                }
            }
        }
        return res;
    }
    
    private void solve(boolean[][] grid,int x,int y){
        if(x<0 || x>=grid.length || y<0 || y>=grid[x].length) return ;
        
        if(!grid[x][y]) return ;
        grid[x][y]=false;
        
        solve(grid,x+1,y);
        solve(grid,x-1,y);
        solve(grid,x,y+1);
        solve(grid,x,y-1);
    }
    
}