leetcode743. 网络延迟时间

朴素Dijksra

class Solution {
public:
    int networkDelayTime(vector<vector<int>>& times, int n, int k) {
        int inf=INT_MAX/2;
        vector<vector<int>>g(n+1,vector<int>(n+1,inf));
        for(auto t:times){//初始化图
            g[t[0]][t[1]]=t[2];
        }
        vector<int>dist(n+1,inf);
        dist[k]=0;
        vector<int>used(n+1);
        for(int i=1;i<=n;i++){
            int t=-1;
            for(int j=1;j<=n;++j){
                 if(!used[j]&&(t==-1||dist[j]<dist[t]))t=j;//找到最小距离点
            }
            used[t]=true;
           for(int k=1;k<=n;k++){
               dist[k]=min(dist[t]+g[t][k],dist[k]);//更新距离
           }
        }
        int ans=*max_element(dist.begin()+1,dist.end());
        return ans==inf?-1:ans;
    }
};

堆优化Dijtsra

class Solution {
public:
    int h[110],ne[6010],e[6010],w[6010],idx;
    int networkDelayTime(vector<vector<int>>& times, int n, int k) {
        int inf=INT_MAX/2;
        memset(h,-1,sizeof h);
        for(auto t:times){
            w[idx]=t[2];
            e[idx]=t[1];
            ne[idx]=h[t[0]];
            h[t[0]]=idx++;
        }
        vector<int>dist(n+1,inf);
        dist[k]=0;
        priority_queue<pair<int,int>,vector<pair<int,int>>,greater<pair<int,int>>> q;//小根堆
        q.push({0,k});
        vector<int>used(n+1,0);
        while(q.size()){
            auto t=q.top();
            q.pop();
            int ver=t.second,distence=t.first;
            if(used[ver])continue;
            used[ver]=true;
            for(int i=h[ver];i!=-1;i=ne[i]){
                int j=e[i];
                if(dist[j]>w[i]+dist[ver]){
                    dist[j]=w[i]+dist[ver];
                    q.push({dist[j],j});
                }
            }
        }
        int ans=*max_element(dist.begin()+1,dist.end());
        return ans==inf?-1:ans;
    }
};

Bellman-Ford算法

class Solution {
public:
    int h[110],ne[6010],e[6010],w[6010],idx;
    int networkDelayTime(vector<vector<int>>& times, int n, int k) {
        int inf=INT_MAX/2;
        vector<int>dist(n+1,inf);
        dist[k]=0;
        for(int i=0;i<n;++i){
            for(auto t:times){
                dist[t[1]]=min(dist[t[1]],dist[t[0]]+t[2]);
            }
        }
        int ans=*max_element(dist.begin()+1,dist.end());
        return ans==inf?-1:ans;
    }
};

Floyd算法

class Solution {
public:
    int networkDelayTime(vector<vector<int>>& times, int n, int k) {
        int inf=INT_MAX/2;
        vector<vector<int>>d(n+1,vector<int>(n+1,inf));
        for(int i=1;i<=n;i++)
            for(int j=1;j<=n;j++)
                if(i==j)d[i][j]=0;
        for(auto t:times){
            d[t[0]][t[1]]=t[2];
        }
        for(int u=1;u<=n;++u)
           for(int i=1;i<=n;++i)
                for(int j=1;j<=n;++j)
                    d[i][j]=min(d[i][j],d[i][u]+d[u][j]);
        int ans=0;
        for(int i=1;i<=n;i++){
            ans=max(d[k][i],ans);
        }
        return ans==inf?-1:ans;
    }
};

spfa算法

class Solution {
public:
    int h[110],ne[6010],e[6010],w[6010],idx;
    int networkDelayTime(vector<vector<int>>& times, int n, int k) {
        int inf=INT_MAX/2;
        memset(h,-1,sizeof h);
        for(auto t:times){
            w[idx]=t[2];
           e[idx]=t[1];
           ne[idx]=h[t[0]];
           h[t[0]]=idx++;
        }
        vector<int>dist(n+1,inf);
        dist[k]=0;
        queue<int>q;
        q.push(k);
        vector<int>used(n+1);
        used[k]=true;
        while(q.size()){
            int t=q.front();
            q.pop();
            used[t]=false;
            for(int i=h[t];i!=-1;i=ne[i]){
                int j=e[i];
                if(dist[j]>dist[t]+w[i]){
                    dist[j]=dist[t]+w[i];
                    if(!used[j]){
                        used[j]=true;
                        q.push(j);
                    }
                }
            }
        }
        int ans=*max_element(dist.begin()+1,dist.end());
        return ans==inf?-1:ans;
    }
};