【剑指Offer 13】机器人的运动范围

深度优先

/**
 * 剑指 Offer 13. 机器人的运动范围
 * https://leetcode.cn/problems/ji-qi-ren-de-yun-dong-fan-wei-lcof/
 * 
 * 思路：深度优先
 * */
public class Solution1 {
    private boolean[][] marked;
    private int m;
    private int n;
    private int k;

    public int movingCount(int m, int n, int k) {
        this.m = m;
        this.n = n;
        this.k = k;
        marked = new boolean[m][n];
        return dfs(0, 0);
    }

    private int dfs(int i, int j) {
        if (i < 0 || i >= m || j < 0 || j >= n) {
            return 0;
        }
        if (marked[i][j] || sum(i, j) > k) {
            return 0;
        }
        marked[i][j] = true;
        return dfs(i + 1, j)
                + dfs(i - 1, j)
                + dfs(i, j + 1)
                + dfs(i, j - 1)
                + 1;
    }

    private int sum(int i, int j) {
        String num = String.valueOf(i) + String.valueOf(j);
        int sum = 0;
        for (int index = 0; index < num.length(); index++) {
            sum += num.charAt(index) - '0';
        }
        return sum;
    }
}

更高效地计算下标和：

if (marked[i][j] || sum(i) + sum(j) > k) {
    return 0;
}

private int sum(int num) {
    int sum = 0;
    while (num > 0) {
        sum += num % 10;
        num /= 10;
    }
    return sum;
}

广度优先

/**
 * 剑指 Offer 13. 机器人的运动范围
 * https://leetcode.cn/problems/ji-qi-ren-de-yun-dong-fan-wei-lcof/
 *
 * 思路：广度优先
 * */
public class Solution2 {
    private int m;
    private int n;
    private int k;
    private boolean[][] marked;

    public int movingCount(int m, int n, int k) {
        this.m = m;
        this.n = n;
        this.k = k;
        marked = new boolean[m][n];

        return bfs(0, 0);
    }

    private int bfs(int i, int j) {
        Queue<int[]> queue = new ArrayDeque<>();
        int count = add(queue, i, j);
        while (!queue.isEmpty()) {
            int[] point = queue.remove();
            i = point[0];
            j = point[1];
            count += add(queue, i + 1, j)
                    + add(queue, i - 1, j)
                    + add(queue, i, j + 1)
                    + add(queue, i, j - 1);
        }
        return count;
    }

    private int add(Queue<int[]> queue, int i, int j) {
        if (i < 0 || i >= m || j < 0 || j >= n || marked[i][j] || sum(i) + sum(j) > k) {
            return 0;
        }
        queue.add(new int[]{i, j});
        marked[i][j] = true;
        return 1;
    }

    private int sum(int num) {
        int sum = 0;
        while (num > 0) {
            sum += num % 10;
            num /= 10;
        }
        return sum;
    }
}