Codeforces - 65D - Harry Potter and the Sorting Hat - 简单搜索

https://codeforces.com/problemset/problem/65/D

哈利波特！一种新思路的状压记忆化dfs，记得每次dfs用完要减回去。而且一定是要在dfs外部进行加减！防止在中间return的时候忘记弄回来。用哈希记录状态实现真正的记忆化。

#include<bits/stdc++.h>
using namespace std;
#define ll long longint n;
char s[10005];ll getID(int a[]){ll res=0;for(int i=0;i<4;i++){res=res*10000+a[i];}return res;
}int a[4]={};
int c[4]={};set<ll> se;int dfs(int i){ll ID=getID(a);if(se.count(ID))return 0;else{se.insert(ID);//printf("%d-%lld\n",i,ID);if(i==n){int minnum=*min_element(a,a+4);for(int j=0;j<4;j++){if(a[j]==minnum){c[j]=1;}}return 0;}}if(s[i]!='?'){switch (s[i]){case 'G':a[0]++;dfs(i+1);a[0]--;break;case 'H':a[1]++;dfs(i+1);a[1]--;break;case 'R':a[2]++;dfs(i+1);a[2]--;break;case 'S':a[3]++;dfs(i+1);a[3]--;}}else{int minnum=*min_element(a,a+4);for(int j=0;j<4;j++){if(a[j]==minnum){//cout<<"j="<<j<<endl;a[j]++;dfs(i+1);a[j]--;}}}
}int main(){scanf("%d",&n);scanf("%s",s);dfs(0);//printf("%d\n",se.size());if(c[0])puts("Gryffindor");if(c[1])puts("Hufflepuff");if(c[2])puts("Ravenclaw");if(c[3])puts("Slytherin");}