207. Course Schedule ，210. Course Schedule II (拓扑排序，BFS等)

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207. Course Schedule

题目地址：https://leetcode.com/problems/course-schedule/

求解思路

节点的入度，出度
AOE网的拓扑排序算法

ac代码

class Solution {public:    vector<int> in_degree; // 入度    vector<vector<int>> adj_table; //邻接表    int n;    bool top(int n)    {        int num = 0;        while (num < n)        {            int i = 0;            while (i < n && in_degree[i] != 0){                i++;            }            if (i >= n){                return false;            }            num++;            in_degree[i] = -2; // 删除该节点，相应的入度减1            int len = adj_table[i].size();            for (int j = 0; j < len; j++){                in_degree[adj_table[i][j]] --;            }        }        return true;    }    bool canFinish(int numCourses, vector<pair<int, int>>& prerequisites) {        in_degree = vector<int>(numCourses, 0);//包括孤立点在内，in_degree=0        adj_table.resize(numCourses);        vector<pair<int, int>>::iterator it = prerequisites.begin();        while (it != prerequisites.end())        {               in_degree[it->second] ++;            adj_table[it->first].push_back(it->second);            ++it;        }        return top(numCourses);    }};

210. Course Schedule II

题目地址

https://leetcode.com/problems/course-schedule-ii/

求解思路

在上一题基础上，需要求出序列
因为只要求出满足要求的一个解就行了，所以仍然可以按照上题的求解思路

ac代码如下

class Solution {public:    vector<int> in_degree; // 入度    vector<vector<int>> adj_table; //邻接表    vector<int> ans;    bool flag;    bool top(int n)    {        int num = 0;        while (num < n)        {            int i = 0;            while (i < n && in_degree[i] != 0){                i++;            }            if (i >= n){                return false;            }            ans.push_back(i);            num++;            in_degree[i] = -2; // 删除该节点，相应的入度减1            int len = adj_table[i].size();            for (int j = 0; j < len; j++){                in_degree[adj_table[i][j]] --;            }        }        return true;    }    vector<int> findOrder(int numCourses, vector<pair<int, int>>& prerequisites) {        in_degree = vector<int>(numCourses, 0);//包括孤立点在内，in_degree=0        adj_table.resize(numCourses);        vector<pair<int, int>>::iterator it = prerequisites.begin();        while (it != prerequisites.end())        {            in_degree[it->second] ++;            adj_table[it->first].push_back(it->second);            ++it;        }        vector<int> rs;        if (top(numCourses))        {            rs.assign(ans.rbegin(), ans.rend());        }        return rs;    }};

超时，超内存代码

dfs求解，可以得到所有的解，代码超时

class Solution {public:    vector<int> in_degree; // 入度    vector<vector<int>> adj_table; //邻接表    int n;    vector<int> ans;    vector<bool> vis;    bool flag;    vector<int> rs;    void top(int cnt)    {        if (flag)            return;        if(cnt > 0)        {            vector<int> in_d0;            int in_len = 0;            for (int i = 0; i < n; i++)            {                if (!vis[i] && in_degree[i] == 0)                {                    in_d0.push_back(i);                    in_len++;                }            }            if (in_len == 0)            {                return;            }            for (int i = 0; i < in_len; i++)            {                int po = in_d0[i];                int tmp = in_degree[po];                in_degree[po] = -2; // 删除该节点，相应的入度减1                vis[po] = true;                int len = adj_table[po].size();                for (int j = 0; j < len; j++){                    in_degree[adj_table[po][j]] --;                }                ans.push_back(po);                top(cnt - 1); // 递归 回溯                if (flag)                    return;                int ansLen = ans.size();                if (ansLen == n)                {                    /*for (int k = 0; k < n; k++)                        cout << ans[k] << " ";                    cout << endl;*/                    flag = true;                    rs.assign(ans.rbegin(), ans.rend());                    return;                }                ans.pop_back();                in_degree[po] = tmp;                vis[po] = false;                for (int j = 0; j < len; j++){                    in_degree[adj_table[po][j]] ++;                }            }        }        return;    }    vector<int> findOrder(int numCourses, vector<pair<int, int>>& prerequisites) {        in_degree = vector<int>(numCourses, 0);//包括孤立点在内，in_degree=0        adj_table.resize(numCourses);        vector<pair<int, int>>::iterator it = prerequisites.begin();        while (it != prerequisites.end())        {            in_degree[it->second] ++;            adj_table[it->first].push_back(it->second);            ++it;        }        n = numCourses;        vis = vector<bool>(numCourses, false);        flag = false;        top(n);        if (flag)            return rs;        return vector<int>();    }};

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