Leetcode LCP-07

public int numWays(int n, int[][] relations, int k) {
        int cnt = 0;
        boolean[][] isVisited = new boolean[n][n];//判断是否经过

        for (int[] relation : relations) {
            isVisited[relation[0]][relation[1]] = true;
        }

        return dfs(0 , isVisited , k);
    }

    public int dfs(int n , boolean[][] isVisited , int k){
        if (k == 0){
            return isVisited.length - 1 == n ? 1 : 0;
        }

        int cnt = 0 ;
        for (int i = 0; i < isVisited[n].length; i++) {
            if (isVisited[n][i]){//是则加1
                cnt += dfs(i , isVisited , k - 1);//递归
            }
        }

        return cnt;
    }