Write a method to compute all permutations of a string

其實就是全排列。

#include <iostream>
#include <vector>
#include <string>
using namespace std;

#define MAXN 100
int N;
bool visit[MAXN];
vector<string>ans;

void dfs_permute(int i, string line, string s)
{
    if (i == N)
    {
        ans.push_back(line);
    }
    for (int k = 0; k < N; k++)
    {
        if(!visit[k])
        {
            visit[k]=true;
            line.push_back(s[k]);
            dfs_permute(i + 1, line, s);
            visit[k]=false;
            line.resize(line.size()-1);
        }
    }
}

int main()
{
    string s="abc";
    N=s.size();
    memset(visit, false, MAXN*sizeof(bool));
    string line;

    dfs_permute(0, line, s);

    for(int i=0; i<ans.size(); i++)
    {
        for(int j=0; j<ans[i].size(); j++)
            cout<<ans[i][j];
        cout<<endl;
    }
    return 0;
}