题目链接：http://poj.org/problem?id=1416
题意：一段数分成好几段相加，求最大的且不大于目标值的组合。
DFS，用vector<int>tmp来记录中间结果，回溯的时候pop掉。判重用了个map，其实用一个flag打标记也可。
1 #include <algorithm> 2 #include <iostream> 3 #include <iomanip> 4 #include <cstring> 5 #include <climits> 6 #include <complex> 7 #include <cassert> 8 #include <cstdio> 9 #include <bitset> 10 #include <vector> 11 #include <deque> 12 #include <queue> 13 #include <stack> 14 #include <ctime> 15 #include <set> 16 #include <map> 17 #include <cmath> 18 19 using namespace std; 20 21 const int maxn = 32; 22 int digit[maxn]; 23 map<int,int> vis; 24 int n, aim; 25 int len, ret; 26 vector<int> ans, tmp; 27 28 int sum(int x, int y) { 29 int ret = 0; 30 while(x <= y) { 31 ret *= 10; 32 ret += digit[x++]; 33 } 34 return ret; 35 } 36 37 void dfs(int cur, int pos) { 38 if(cur > aim) return; 39 if(pos > len) { 40 if(cur <= aim) { 41 if(ret <= cur) { 42 ret = cur; vis[ret]++; 43 ans.clear(); 44 for(int i = 0; i < tmp.size(); i++) { 45 ans.push_back(tmp[i]); 46 } 47 } 48 } 49 return; 50 } 51 for(int i = pos; i <= len; i++) { 52 int x = sum(pos, i); 53 tmp.push_back(x); 54 dfs(cur+x, i+1); 55 tmp.pop_back(); 56 } 57 } 58 59 void f(int x) { 60 len = 0; 61 vector<int> s; 62 while(x) { 63 s.push_back(x%10); 64 x /= 10; 65 } 66 for(int i = s.size() - 1; i >= 0; i--) { 67 digit[++len] = s[i]; 68 } 69 tmp.clear(); 70 dfs(0, 1); 71 } 72 73 int main() { 74 // freopen("in", "r", stdin); 75 while(~scanf("%d%d",&aim,&n)&&aim+n) { 76 if(aim >= n) { 77 printf("%d %d ",n, n); 78 continue; 79 } 80 ret = -1; vis.clear(); 81 f(n); 82 if(ret == -1) puts("error"); 83 else if(vis[ret] >= 2) puts("rejected"); 84 else { 85 printf("%d ", ret); 86 for(int i = 0; i < ans.size(); i++) { 87 if(i) printf(" "); 88 printf("%d", ans[i]); 89 } 90 printf(" "); 91 } 92 } 93 return 0; 94 }
状压枚举也可以
1 #include <algorithm> 2 #include <iostream> 3 #include <iomanip> 4 #include <cstring> 5 #include <climits> 6 #include <complex> 7 #include <cassert> 8 #include <cstdio> 9 #include <bitset> 10 #include <vector> 11 #include <deque> 12 #include <queue> 13 #include <stack> 14 #include <ctime> 15 #include <set> 16 #include <map> 17 #include <cmath> 18 using namespace std; 19 20 const int maxn = 32; 21 int digit[maxn]; 22 int n, m, len, ret; 23 bool dump; 24 vector<int> tmp, ans; 25 26 void f(int x) { 27 len = 0; tmp.clear(); 28 while(x) { 29 tmp.push_back(x % 10); 30 x /= 10; 31 } 32 for(int i = int(tmp.size())-1; i >= 0; i--) { 33 digit[len++] = tmp[i]; 34 } 35 } 36 37 void get(vector<int>& tmp, int sta, int& sum) { 38 int cur = 0, flag = 0; 39 tmp.clear(); sum = 0; 40 cur = digit[0]; 41 flag = sta % 2; sta >>= 1; 42 for(int i = 1; i < len; i++, sta>>=1) { 43 if(sta % 2 == flag) { 44 cur = cur * 10 + digit[i]; 45 } 46 else { 47 flag = !flag; 48 tmp.push_back(cur); sum += cur; 49 cur = digit[i]; 50 } 51 } 52 tmp.push_back(cur); sum += cur; 53 } 54 55 int main() { 56 // freopen("in", "r", stdin); 57 while(~scanf("%d%d",&n,&m) && n+m) { 58 f(m); dump = 0; ans.clear(); ret = -1; 59 int mm = 1 << len, sum; 60 mm >>= 1; 61 for(int sta = 0; sta < mm; sta++) { 62 get(tmp, sta, sum); 63 if(sum > n) continue; 64 if(sum > ret) { 65 ret = sum; dump = 0; 66 ans = tmp; 67 } 68 else if(sum == ret) dump = 1; 69 } 70 if(!~ret) puts("error"); 71 else if(dump) puts("rejected"); 72 else { 73 printf("%d", ret); 74 for(int i = 0; i < ans.size(); i++) { 75 printf(" %d", ans[i]); 76 } 77 printf(" "); 78 } 79 } 80 return 0; 81 }