51nod1693 水群

题目链接：51nod1693 水群

题解参考大神的博客：http://www.cnblogs.com/fighting-to-the-end/p/5874763.html

这题时限0.4秒，真的够狠的。。我用优化过的dij狂交一直TLE，最后还是死在四百多毫秒上，应该是姿势不对orz。后来看别人用spfa，然后一改就过了,这里我想收藏一下记忆化搜索的解法，真心服了。

 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 using namespace std;
 const int N = ;
 const int inf = 0x3f3f3f3f;
 int n;
 int pri[] = {,,,,};
 int s[N][];//1到i上一条边的状态是f的最小操作数
 //j=0时，上一条边可以是i->i-1,否则是i->i*p
 int dfs(int x, int f){
     if(x == ) return ;
     if(s[x][f]) return s[x][f];
     s[x][f] = inf;
     for(int i = ; i < ; i++)
         if(!(x % pri[i]))
             s[x][f] = min(s[x][f], dfs(x /pri[i], ) + pri[i]);
     if(!f) return s[x][f];
     s[x][] = s[x][];
     for(int i = ; i < ; i++)
         s[x][f] = min(s[x][f], dfs( x + i, ) + i);
     return s[x][f];
 }
 int main(){
     scanf("%d", &n);
     printf("%d\n", dfs(n, ));
     return ;
 }

AC代码

再贴上我这份超时了的dij，我写的好差啊，只好说我刚刚入门最短路姿势还不够orz

 #include<cstdio>
 #include<cstring>
 #include<algorithm>
 #include<vector>
 #include<queue>
 #define CLR(a,b) memset((a),(b),sizeof((a)))
 using namespace std;
 #define inf 0x3f3f3f3f
 const int N = ;
 int d[N], vis[N];
 int prime[] = {, , , , };
 int n;
 struct qnode{
     int v,c;
     qnode(int _v=,int _c=):v(_v),c(_c){}
     bool operator < (const qnode &r)const{
         return r.c <c;
     }
 };
 void dij(){
     priority_queue<qnode>q;
     for(int i = ; i <= n+; ++i){
         d[i] = inf;
         vis[i] = ;
     }
     d[]=;
     q.push(qnode(, ));
     while(!q.empty()){
         qnode t=q.top(); q.pop();
         int u=t.v;
         if(vis[u])
             continue;
         vis[u]=;
         for(int i = ; i<  && u * prime[i] <= n+; ++i){
             int v = u * prime[i];
             int w = prime[i];
             if(!vis[v] && d[u] + w < d[v]){
                 d[v] = d[u] + w;
                 q.push(qnode(v, d[v]));
             }
         }
         int v = u - ;
         int w = ;
         if(!vis[v] && d[u] + w < d[v]){
             d[v] = d[u] + w;
             q.push(qnode(v, d[v]));
         }
     }
 }
 int main(){
     scanf("%d", &n);
     dij();
     printf("%d\n", d[n]);
     return ;
 }

TLE代码