待梳理算法

待梳理

 

课程表

https://leetcode-cn.com/problems/course-schedule/solution/course-schedule-tuo-bu-pai-xu-bfsdfsliang-chong-fa/

class Solution {
    public boolean canFinish(int numCourses, int[][] prerequisites) {
        List> adjacency = new ArrayList<>();
        for(int i = 0; i < numCourses; i++)
            adjacency.add(new ArrayList<>());
        int[] flags = new int[numCourses];
        for(int[] cp : prerequisites)
            adjacency.get(cp[1]).add(cp[0]);
        for(int i = 0; i < numCourses; i++)
            if(!dfs(adjacency, flags, i)) return false;
        return true;
    }
    private boolean dfs(List> adjacency, int[] flags, int i) {
        if(flags[i] == 1) return false;
        if(flags[i] == -1) return true;
        flags[i] = 1;
        for(Integer j : adjacency.get(i))
            if(!dfs(adjacency, flags, j)) return false;
        flags[i] = -1;
        return true;
    }
}