input
4
4
0001
1000
0011
0111
3
010
101
0
2
00000
00001
4
01
001
0001
00001
output
1
3
-1
0
2
1 2
题意
给定n个二进制串的集合,要求从第二个串开始每一个串的开头第一个字母必须是上一个
二进制的结尾字符,你可以翻转这n个字符串(翻转后不能出现相同字符),问操作数最
少的情况下翻转那些字符串,使得这n和字符进行排列后可以满足条件
思路
记录zz = 0...0, oo = 1...1, oz = 1...0, zo = 0...1字符串的数量
若!zo && !oz那么:
若!zz || !oo则以及满足条件
其他一定不能满足条件
最少操作次数为abs(zo-oz)/2, 每次将多出来的zo或者oz输出即可
代码
#pragma GCC optimize(2)
#include<unordered_map>
#include<iostream>
#include<algorithm>
#include<cstring>
#include<cstdio>
#include<string>
#include<vector>
#include<queue>
#include<stack>
#include<cmath>
#include<map>
#include<set>
#define Buff ios::sync_with_stdio(false)
#define rush() int Case = 0; int T; cin >> T; while(T--)
#define rep(i, a, b) for(int i = a; i <= b; i ++)
#define per(i, a, b) for(int i = a; i >= b; i --)
#define reps(i, a, b) for(int i = a; b; i ++)
#define clc(a, b) memset(a, b, sizeof(a))
#define Buff ios::sync_with_stdio(false)
#define readl(a) scanf("%lld", &a)
#define readd(a) scanf("%lf", &a)
#define readc(a) scanf("%c", &a)
#define reads(a) scanf("%s", a)
#define read(a) scanf("%d", &a)
#define lowbit(n) (n&(-n))
#define pb push_back
#define sqr(x) x*x
#define rs x<<1|1
#define y second
#define ls x<<1
#define x first
using namespace std;
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int, int>PII;
const int mod = 1e9+7;
const double eps = 1e-6;
const int N = 2e5+7;
string s[N];
int main()
{
rush()
{
int n;
cin >> n;
set<string> seen, bad;
int oz = 0, zo = 0, zz = 0, oo = 0;
rep(i, 0, n-1)
{
cin >> s[i];
string rev(s[i].rbegin(), s[i].rend());
if(s[i][0] == '0' && s[i].back() == '1')
{
zo ++;
if(seen.count(rev))
bad.insert(s[i]), bad.insert(rev);
seen.insert(s[i]);
}
else if(s[i][0] == '1' && s[i].back() == '0')
{
oz ++;
if(seen.count(rev))
bad.insert(rev), bad.insert(s[i]);
seen.insert(s[i]);
}
else if(s[i][0] == '0' && s[i].back() == '0') zz ++;
else oo ++;
}
if(!zo && !oz)
{
if(!oo || !zz) cout << 0 <<"
";
else cout << -1 <<endl;
}
else
{
int res = abs(oz-zo)/2;
cout << res <<endl;
rep(i, 0, n-1)
{
if(!res) break;
if(zo > oz && s[i][0] == '0' && s[i].back() == '1' && !bad.count(s[i]))
{cout << i + 1 <<" "; res --;}
if(oz > zo && s[i][0] == '1' && s[i].back() == '0' && !bad.count(s[i]))
{cout << i + 1 <<" "; res --;}
}
cout << endl;
}
}
return 0;
}