组合的递归与非递归_递归 组合

从n数组中选取m个数

#include<iostream>
#include<string>
#include<vector>
using namespace std;
//递归写法
//从n个元素中选取m个 排列有序 123！=321
void Print(int a[],int b[], int n, int m,vector<int>res)
{
    if (m == 0)
    {
        for (auto it = res.begin(); it != res.end(); it++)
            cout << *it;
        cout << endl;
    }
    else
    {
        for (int i = 0; i < n; i++)
        {
            if (b[i] == 0)
            {
                res.push_back(a[i]);
                b[i] = 1;
                Print(a, b, n, m - 1, res);
                b[i] = 0;
                res.pop_back();
            }

        }
    }

}
//从n个元素中选取m个 排列无序 123=321
void Print1(int a[],int n, int m, int start,vector<int>res)
{
    if (m == 0)
    {
        for (auto it = res.begin(); it != res.end(); it++)
            cout << *it;
        cout << endl;
    }
    else
    {
        for (int i = start; i < n; i++)
        {

                res.push_back(a[i]);

                Print1(a,n, m - 1,i+1,res);

                res.pop_back();

        }
    }

}
//非递归写法  每次从右至左找10组合，交换并使得右边的1是在一起的
/*
11100
11010
11001
10110
10101
10011
01110
01101
01011
00111
*/
void P(int a[], int b[],int n)
{
    for (int i = 0; i < n;i++)
    if (b[i] == 1) cout << a[i];
    cout << endl;
}
void print3(int a[], int n, int m)
{
    int b[5] = { 0 };
    for (int i = 0; i<m; i++)
        b[i] = 1;
    int flag = 1;
    while (flag>0)
    {
        P(a, b, n);
        int count = 0;//从右至左找到10时右边1的个数
        for (flag = n - 1; flag > 0; flag--)
        {
            if (b[flag] == 0 && b[flag - 1] == 1) break;
            if (b[flag]==1)
               count++;
        }
        if (flag > 0)
        {
            swap(b[flag], b[flag - 1]);          //交换10并且使得右边的1是连续的
            for (int i = 0; i <=count; i++)
                b[flag + i] = 1;
            for (int j = flag + count+1; j < n; j++)
                b[j] = 0;
        }
    }
}
int main()
{
    int a[5] = { 1, 2, 3, 4, 5 };
    print3(a, 5, 3);
    return 0;
}
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