一.只需输出一种子集

#include <iostream>
using namespace std;

int s[100];//集合
int s1[100];//解集(0/1)
int s2[100];
int n;//数目
int c;//目标加和
int cw;//当前加和
int r;
int best;
bool flag;

void BackTrack(int i)
{
    if (i > n) {
        if (cw == c) {
             for (int i = 1; i <= n; i++) 
                 s2[i]=s1[i];
             flag = false;
        }
        best = cw;
        return;
     }
    if (cw + s[i] <= c) {
        s1[i] = 1;
        cw += s[i];
        BackTrack(i + 1);
        cw -= s[i];
    }
    r -= s[i];
    if (cw + r > best) {
        s1[i] = 0;
        BackTrack(i + 1);
    }
    r += s[i];
 }
 
int main()
{
    cin >> n;
    r = 0;
    for (int i = 1; i <= n; i++) {
        cin >> s[i];
        r += s[i];
    }
    cin >> c;
    cw = 0;
    best = 0;
    flag = true;
    BackTrack(1);
    if (flag == true)  cout << "No solution" << endl;
    else {
        for (int i = 1; i <= n; i++) 
            if (s2[i] == 1) cout << s[i] << " ";
        cout << endl;
    }
 }

二.所有情况都输出

#include <iostream>
using namespace std;

int s[100];//集合
int s1[100];//解集(0/1)
int n;//数目
int c;//目标加和
int cw;//当前加和
int r;
int best;
bool flag;

void BackTrack(int i)
{
    if (i > n) {
        if (cw == c) {
            for (int i = 1; i <= n; i++) 
                if (s1[i] == 1) cout << s[i] << " ";
            cout << endl;
            flag = false;
        }
        best = cw;
        return;
    }
    if (cw + s[i] <= c) {
        s1[i] = 1;
        cw += s[i];
        BackTrack(i + 1);
        cw -= s[i];
    }
    r -= s[i];
    if (cw + r > best) {
        s1[i] = 0;
        BackTrack(i + 1);
    }
    r += s[i];
 }
 int main()
 {
    cin >> n;
    r = 0;
    for (int i = 1; i <=n; i++) {
        cin >> s[i];
        r += s[i];
    }
    cin >> c;
    cw = 0;
    best = 0;
    flag = true;
    BackTrack(1);
    if (flag == true)  cout << "No solution" << endl;
 }