链接：
https://codeforces.com/contest/1251/problem/B
题意：
A palindrome is a string t which reads the same backward as forward (formally, t[i]=t[|t|+1−i] for all i∈[1,|t|]). Here |t| denotes the length of a string t. For example, the strings 010, 1001 and 0 are palindromes.
You have n binary strings s1,s2,…,sn (each si consists of zeroes and/or ones). You can swap any pair of characters any number of times (possibly, zero). Characters can be either from the same string or from different strings — there are no restrictions.
Formally, in one move you:
choose four integer numbers x,a,y,b such that 1≤x,y≤n and 1≤a≤|sx| and 1≤b≤|sy| (where x and y are string indices and a and b are positions in strings sx and sy respectively),
swap (exchange) the characters sx[a] and sy[b].
What is the maximum number of strings you can make palindromic simultaneously?
思路:
考虑所有串的长度，当有奇数长度存在时，保证可以交换出全部，当没有时， 可能存在0或1为奇数，不能配对，有奇数可以将奇数减位，同时保证剩下的偶数相等。
代码：
#include<bits/stdc++.h>
using namespace std;
typedef long long LL;
int n;
string s;
int main()
{
int t;
scanf("%d", &t);
while(t--)
{
int one = 0, zer = 0;
int q = 0;
scanf("%d", &n);
for (int i = 1;i <= n;i++)
{
cin >> s;
int len = (int)s.length();
if (len%2)
q++;
for (int j = 0;j < len;j++)
{
if (s[j] == '0')
zer++;
else
one++;
}
}
if (q > 0)
printf("%d\n", n);
else
{
if (one%2 || zer%2)
printf("%d\n", n-1);
else
printf("%d\n", n);
}
}
return 0;
}