给定一个由 '1'（陆地）和 '0'（水）组成的的二维网格，计算岛屿的数量。一个岛被水包围，并且它是通过水平方向或垂直方向上相邻的陆地连接而成的。你可以假设网格的四个边均被水包围。
示例 1:
输入:
11110
11010
11000
00000
输出: 1
示例 2:
输入:
11000
11000
00100
00011
输出: 3
链接：https://leetcode-cn.com/problems/number-of-islands
public class NumIslands {
public int numIslands(char[][] grid) {
if (grid == null || grid.length == 0 || grid[0].length == 0) {
return 0;
}
int row = grid.length;
int col = grid[0].length;
int num = 0;
for (int i = 0; i < row; i++) {
for (int j = 0; j < col; j++) {
if (grid[i][j] == '1') {
num++;
search(grid, i, j, row, col);
}
}
}
return num;
}
private void search(char[][] grid, int x, int y, int row, int col) {
if (x < 0 || x >= row || y < 0 || y >= col || grid[x][y] != '1') {
return;
}
grid[x][y] = '2';
search(grid, x - 1, y, row, col);
search(grid, x + 1, y, row, col);
search(grid, x, y - 1, row, col);
search(grid, x, y + 1, row, col);
}
}==============================================================================
N皇后问题
public class Nqueue {
private boolean[] col;
private boolean[] dia1;
private boolean[] dia2;
private ArrayList<List<String>> res = new ArrayList<>();
public static void main(String[] args) {
int n = 4;
List<List<String>> res = (new Nqueue()).solveNqueues(n);
for (List<String> board : res) {
printBoard(board);
}
}
private static void printBoard(List<String> board) {
for (String s : board)
System.out.println(s);
System.out.println();
}
public List<List<String>> solveNqueues(int n) {
col = new boolean[n];
dia1 = new boolean[2 * n - 1];
dia2 = new boolean[2 * n - 1];
LinkedList<Integer> row = new LinkedList<Integer>();
putQueen(n, 0, row);
return res;
}
private void putQueen(int n, int index, LinkedList<Integer> row) {
if (index == n) {
res.add(generateBoard(n, row));
return;
}
for (int i = 0; i < n; i++) {
if (!col[i] && !dia1[index + i] && !dia2[index - i + n - 1]) {
row.add(i);
col[i] = true;
dia1[index + i] = true;
dia2[index - i + n - 1] = true;
putQueen(n, index + 1, row);
col[i] = false;
dia1[index + i] = false;
dia2[index - i + n - 1] = false;
row.removeLast();
}
}
}
private List<String> generateBoard(int n, LinkedList<Integer> row) {
assert (row.size() == n);
ArrayList<String> board = new ArrayList<>();
for (int i = 0; i < n; i++) {
char[] charArray = new char[n];
Arrays.fill(charArray, '.');
charArray[row.get(i)] = 'Q';
board.add(new String(charArray));
}
return board;
}
}
