Python3 解法, 执行用时: 43ms, 内存消耗: 6812K, 提交时间: 2023-08-06 18:14:30

def main():
    stro = input();
    digi_dict = {};
    ordlist = [];

    for digi in stro:
        digi_dict[digi] = digi_dict.get(digi,0) + 1;
    for digi in digi_dict.keys():
        if(digi_dict[digi]%2==1):
            ordlist.append(digi);
            digi_dict[digi] -= 1;
    if(len(ordlist)<=1):
        print(1);
    else:
        print(len(ordlist));

    mainstr = '';
    keylist = list(digi_dict.keys());
    M = len(digi_dict.keys());
    for i in range(M):
        mainstr += keylist[i]*(digi_dict[keylist[i]]//2);
    if(ordlist):
        mainstr += ordlist.pop();
    for i in range(M):
        mainstr += keylist[-i-1]*(digi_dict[keylist[-i-1]]//2);

    print(mainstr);
    for digi in ordlist:
        print(digi);

    return;

main();

C++ 解法, 执行用时: 4ms, 内存消耗: 460K, 提交时间: 2021-12-01 18:57:57

#include<bits/stdc++.h>
using namespace std;
const int N=1e3+100;
char s[N];
int ans,num[N],a[N];

int main()
{
	scanf("%s",s);
	int n=strlen(s);
	for(int i=0;i<n;i++)
		num[(s[i]-'a'+1)]++;
	
	for(int i=1;i<=26;i++)
	{
		if(num[i]%2)
		{
			ans+=1;
			a[ans]=i;
		}
	}
	
	printf("%d\n",max(ans,1));
	for(int i=1;i<=26;i++)
	{
		int w=num[i]/2;
		for(int j=1;j<=w;j++)
			printf("%c",(i-1)+'a');
	}
	if(ans)
		printf("%c",a[1]-1+'a');
	for(int i=26;i>=1;i--)
	{
		int w=num[i]/2;
		for(int j=1;j<=w;j++)
			printf("%c",(i-1)+'a');
	}
	printf("\n");
	for(int i=2;i<=ans;i++)
		printf("%c\n",a[i]-1+'a');
	
	return 0;
}