算法修炼Day30|● 332.重新安排行程 ● 51. N皇后

题目：332. 重新安排行程 - 力扣（LeetCode）

代码实现：

class Solution {
    private LinkedList<String> res;
    private LinkedList<String> path = new LinkedList<>();

    public List<String> findItinerary(List<List<String>> tickets) {
        Collections.sort(tickets, (a, b) -> a.get(1).compareTo(b.get(1)));
        path.add("JFK");
        boolean[] used = new boolean[tickets.size()];
        backtracking((ArrayList)tickets, used);
        return res;
    }
    public boolean backtracking(ArrayList<List<String>> tickets, boolean[] used) {
        if (path.size() == tickets.size() + 1) {
            res = new LinkedList(path);
            return true;
        }
        for (int i = 0; i < tickets.size(); i++) {
            if (!used[i] && tickets.get(i).get(0).equals(path.get(path.size() - 1))) {
                path.add(tickets.get(i).get(1));
                used[i] = true;
                if (backtracking(tickets, used)) return true;
                used[i] = false;
                path.remove(path.size() - 1);
            }
        }
        return false;
    }
}

题目：51. N 皇后 - 力扣（LeetCode）

代码实现：

class Solution {
    List<List<String>> res = new ArrayList<>();
    public List<List<String>> solveNQueens(int n) {
        char[][] chessboard = new char[n][n];
        for (char[] c : chessboard) {
            Arrays.fill(c, '.');
        }
        backtracking(n, 0, chessboard);
        return res;
    }
    public void backtracking(int n, int row, char[][] chessboard) {
        if (row == n) {
            res.add(ArrayList(chessboard));
            return;
        }
        for (int col = 0; col < n; col++) {
            if (isValid(row, col, n, chessboard)) {
                chessboard[row][col] = 'Q';
                backtracking(n, row + 1, chessboard);
                chessboard[row][col] = '.';
            }
        }
    }
    public List ArrayList(char[][] chessboard) {
        List<String> list = new ArrayList<>();
        for (char[] c : chessboard) {
            list.add(String.copyValueOf(c)); // 将字符数组转换为字符串并加入结果集
        }
        return list;
    }
    public boolean isValid(int row, int col, int n, char[][] chessboard) {
        // 检查列
        for (int i = 0; i < row; i++) {
            if (chessboard[i][col] == 'Q') return false;
        }
        // 检查135度对角线
        for (int i = row - 1, j = col - 1; i >= 0 && j >= 0; i--, j--) {
            if (chessboard[i][j] == 'Q') return false;
        }
        // 检查45度对角线
        for (int i = row - 1, j = col + 1; i >= 0 && j <= n - 1; i--, j++) {
            if (chessboard[i][j] == 'Q') return false;
        }
        return true;
    }
}