HackerRank Palindromes

题目在这里

https://www.hackerrank.com/challenges/palindromes

用到了高斯消元

#include "stdio.h"
#include <iostream>
#include <cmath>
#include <vector>
#include <queue>
#include <map>
#include <algorithm>
#include "string.h"
using namespace std;
double Matrix[1000][1000];
string Normalize(string s){
string res;
int num[26],val=0;
memset(num,-1,sizeof(num));
for(int i=0;i<s.size();i++){
if(num[s[i]-'a']==-1)
num[s[i]-'a']=val++;
res.push_back(('a'+num[s[i]-'a']));
}
return res;
}
map<string,int> ids;
map<string,double> ans;
double solve(string s){
s=Normalize(s);
if(ans.find(s)!=ans.end())
return ans[s];

ids.clear();
string next=s;
sort(next.begin(),next.end());
do{
string next_s=Normalize(next);
if(ids.find(next_s)==ids.end()){
int size=ids.size();
ids[next_s]=size;
}

}while(next_permutation(next.begin(),next.end()));

int N=ids.size(), len=s.size(), swapSize=len*(len-1)/2;
for(int i=0;i<=N;i++)
for(int j=0;j<=N;j++)
Matrix[i][j]=0;
for(map<string,int>::iterator it=ids.begin();it!=ids.end();it++){
string str=it->first;
int id=it->second;
if(Matrix[id]
!=0) continue;
Matrix[id]
=Matrix[id][id]=1;
string tmp=str;
reverse(tmp.begin(),tmp.end());
if(tmp==str){
Matrix[id]
=0;
continue;
}
for(int i=0;i<len;i++){
for(int j=i+1;j<len;j++){
swap(str[i],str[j]);
int id2=ids[Normalize(str)];
Matrix[id][id2]-=1.0/swapSize;
swap(str[i],str[j]);
}
}
}

for(int i=0;i<N;i++){
for(int j=N;j>=i;j--) Matrix[i][j]/=Matrix[i][i];
for(int j=0;j<N;j++){
if(i!=j){
for(int k=N;k>=i;k--)
Matrix[j][k]-=Matrix[i][k]*Matrix[j][i];
}
}
}

for(map<string,int>::iterator it=ids.begin();it!=ids.end();it++){
string str=it->first;
int id=it->second;
if(ans.find(str)==ans.end())
ans[str]=Matrix[id]
;

}
return ans[s];
}
int main(){
int T;
scanf("%d",&T);
for(int t=0;t<T;t++){
string str;
cin>>str;
printf("%.4lf\n",solve(str));
}
}