PAT甲级——A1038 Recover the Smallest Number

Given a collection of number segments, you are supposed to recover the smallest number from them. For example, given { 32, 321, 3214, 0229, 87 }, we can recover many numbers such like 32-321-3214-0229-87 or 0229-32-87-321-3214 with respect to different orders of combinations of these segments, and the smallest number is 0229-321-3214-32-87.

Input Specification:

Each input file contains one test case. Each case gives a positive integer N (≤) followed by N number segments. Each segment contains a non-negative integer of no more than 8 digits. All the numbers in a line are separated by a space.

Output Specification:

For each test case, print the smallest number in one line. Notice that the first digit must not be zero.

Sample Input:

5 32 321 3214 0229 87

Sample Output:

22932132143287

#include <iostream>
#include <string>
#include <vector>
#include <algorithm>
using namespace std;
//排序问题
int N;
vector<string>v, temp;
string res = "", str = "";
void permuteDFS(int u,vector<bool>&visit)//使用DFS
{
    if (u == v.size())
    {
        for (auto a : temp)
            str += a;
        res = res > str ? str : res;
        str = "";
        return;
    }
    for (int i = 0; i < N; ++i)
    {
        if (visit[i] == true)continue;
        visit[i] = true;
        temp.push_back(v[i]);
        permuteDFS(i + 1, visit);
        temp.pop_back();
        visit[i] = false;
    }
}

void permutex(int u)//使用递归
{
    if (u == v.size())
    {
        for (auto a : v)
            str += a;
        res = res > str ? str : res;
        str = "";
    }
    for (int i = u; i < N; ++i)
    {
        swap(v[i], v[u]);
        permutex(i + 1);
        swap(v[i], v[u]);
    }
}

void Sort()//使用排序法则
{
    sort(v.begin(), v.end(), [](string a, string b) {return a + b < b + a; });
    res = "";
    for (auto a : v)
        res += a;
}

int main()
{
    cin >> N;
    v.resize(N);
    vector<bool>visit(N, false);
    for (int i = 0; i < N; ++i)
    {
        cin >> v[i];
        res += v[i];
    }
    //permutex(0);
    //permuteDFS(0, visit);
    Sort();
    while (!res.empty() && res[0] == '0')
        res.erase(0, 1);
    if (res.size() == 0)cout << 0;
    cout << res << endl;
    return 0;
}