结构体二级排序，准则是其逆序数，按照题意来即可，么有压力。

#include <iostream>
#include <string>
#include <algorithm>

using namespace std;

struct dna
{
    int num;
    string s;
}DNA[105];

int inversionNum(string s)
{
    int ans = 0;
    int A, C, G;
    A = C = G = 0;
    for(int i = s.length() - 1; i >= 0; i--)
    {
        switch (s[i]) {
            case ‘A‘:
                A++;
                break;
            case ‘C‘:
                C++;
                ans += A;
                break;
            case ‘G‘:
                G++;
                ans += A;
                ans += C;
                break;
            case ‘T‘:
                ans += A;
                ans += C;
                ans += G;
        }
    }
    return ans;
}

bool operator < (struct dna a, struct dna b)
{
    return a.num < b.num;
}

int main()
{
    int n, m;
    while (cin>>n>>m) {
        for (int i = 0; i < m; i++) {
            cin>>DNA[i].s;
            DNA[i].num = inversionNum(DNA[i].s);
        }
        sort(DNA, DNA+m);
        for (int i = 0; i < m; i++) {
            cout << DNA[i].s << endl;
        }
    }
}

poj1007