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207-canFinish.h
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157 lines (135 loc) · 3.26 KB
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#pragma once
#include <iostream>
#include <vector>
#include <map>
#include <math.h>
#include <algorithm>
#include <queue>
using namespace std;
class CSolution
{
public:
bool canFinish_BFS(int numCourse, vector<pair<int, int>>& prerequies);
bool canFinish_DFS(int numCourses, vector<pair<int, int>>& prerequies);
bool canFinish(int numCourses, vector<pair<int, int>>& prerequies);
protected:
private:
};
// BFS 图的入度和出度 判断是否有环
bool CSolution::canFinish_BFS(int numCourse, vector<pair<int, int>>& prerequies)
{
vector<vector<int>> Graph(numCourse, vector<int>(0));
vector<int> inDegree(numCourse, 0);
for (auto i: prerequies)
{
Graph[i.second].push_back(i.first);
inDegree[i.first]++;
}
queue<int> q;
for (int i = 0; i < inDegree.size(); ++i)
{
if (inDegree[i] == 0)
q.push(i);
}
while (!q.empty())
{
int temp = q.front();
q.pop();
for (auto j:Graph[temp])
{
inDegree[j]--;
if (inDegree[j] == 0)
q.push(j);
}
}
for (int i = 0; i < inDegree.size(); ++i)
{
if (inDegree[i] != 0)
return false;
}
return true;
}
//DFS
/**
* 能否完成所有的课程
* dfs拓扑排序,看有向图是否存在环
* @param numCourses 课程数量
* @param prerequisites 课程先序关系
* @return 能完成返回true,否则false
*/
bool CSolution::canFinish_DFS(int numCourses, vector<pair<int, int>>& prerequisites)
{
vector<int> heads(numCourses, -1), degree(numCourses, 0), points, args;
pair<int, int> p;
int from, to, count = 0, len = prerequisites.size();
/* 构造有向图,邻接表 */
for (int i = 0; i < len; ++i) {
p = prerequisites[i];
from = p.second;
to = p.first;
++degree[from];
args.push_back(heads[to]);
points.push_back(from);
heads[to] = count++;
}
/* dfs拓扑排序,依次移除出度为0的点 */
queue<int> q;
for (int i = 0; i < numCourses; ++i)
if (degree[i] == 0) q.push(i);
while (!q.empty()) {
to = q.front();
q.pop();
from = heads[to];
while (from != -1)
{
if (--degree[points[from]] == 0)
q.push(points[from]);
from = args[from];
}
}
/* 判定是否所有的点入度都为0,若是则不存在环,否则存在环 */
for (int i = 0; i < numCourses; ++i)
if (degree[i] > 0)
return false;
return true;
}
bool CSolution::canFinish(int numCourses, vector<pair<int, int>>& prerequies)
{
vector<vector<int>> matrixCourse(numCourses, vector<int>(numCourses, 0));
vector<int> beforeNeedCourse(numCourses, 0);//标记该课程前置课程数量
vector<bool> flag(numCourses, false);
vector<int> learnCourseOrder;
int nSize = prerequies.size();
for (int i = 0; i < nSize; ++i)
{
beforeNeedCourse[prerequies[i].first]++;
matrixCourse[prerequies[i].second][prerequies[i].first] = 1;
}
queue<int> myQueue;
for (int i = 0; i < nSize; ++i)
{
//找出不需要前提条件的课程
if (beforeNeedCourse[i] == 0)
myQueue.push(i);
}
while (!myQueue.empty())
{
int nTmp = myQueue.front();
myQueue.pop();
flag[nTmp] = true;
learnCourseOrder.push_back(nTmp); //BFS 搜索
//将所有为学习，但需要先学习nTmp的这个课程单独先决条件去除
for (int i = 0; i < numCourses; ++i)
{
if (matrixCourse[nTmp][i] < 0)continue;
matrixCourse[nTmp][i]--;
if (matrixCourse[nTmp][i] == 0 && flag[nTmp] == false)
{
if(--beforeNeedCourse[i]) //减少一个前提条件
continue;
myQueue.push(i);
}
}
}
return learnCourseOrder.size() == numCourses;
}