“借鉴”了别人的代码，优化十分巧妙——只需递归前两个数，就可知道能不能凑一个第三个数使这种情况成立。
1 #include <bits/stdc++.h> 2 #define _for(i,a,b) for(int i = (a);i < (b);i ++) 3 #define pb push_back 4 using namespace std; 5 //-2 stands for the blank ;-1 stands for the * 6 vector<int> p[3]; 7 8 bool ok() 9 { 10 int d[2] {0}; 11 _for(i,0,2) 12 _for(j,0,p[i].size()) 13 if(p[i][j]==-1) 14 return false; 15 else 16 d[i] = d[i]*10+p[i][j]; 17 18 int num = d[0]*d[1]; 19 int str[39]; 20 21 _for(i, 0, p[2].size()) 22 { 23 str[p[2].size()-i-1] = num % 10; 24 num /= 10; 25 } 26 27 if(num != 0 || str[0] == 0) return 0; 28 _for(i, 0, p[2].size()) 29 if(p[2][i] != -1 && str[i] != p[2][i]) 30 return 0; 31 32 return 1; 33 } 34 35 int dfs1(int i,int j) 36 { 37 if(i==2) 38 return ok(); 39 int rnt = 0; 40 if(p[i][j]==-1) 41 { 42 _for(k,0,10) 43 { 44 if(k==0&&j==0) 45 continue; 46 p[i][j] = k; 47 if(j==p[i].size()-1) 48 { 49 rnt += dfs1(i+1,0); 50 p[i][j] = -1; 51 if(rnt>1) return 2; 52 } 53 else 54 { 55 rnt += dfs1(i,j+1); 56 p[i][j] = -1; 57 if(rnt>1) return 2; 58 } 59 } 60 } 61 else 62 { 63 if(j==p[i].size()-1) 64 { 65 rnt += dfs1(i+1,0); 66 if(rnt>1) return 2; 67 } 68 else 69 { 70 rnt += dfs1(i,j+1); 71 if(rnt>1) return 2; 72 } 73 } 74 return rnt; 75 } 76 77 int maxd; 78 const char* word = "*0123456789"; 79 bool dfs2(int i,int j,int d) 80 { 81 if(d==maxd) return (dfs1(0,0)==1); 82 if(i==3) return false; 83 84 int ti, tj; 85 if(j == p[i].size() - 1){ti = i + 1;tj = 0;} 86 else{ti = i;tj = j + 1;} 87 88 char t; 89 if(p[i][j]==-1) 90 t = '*'; 91 else 92 t = p[i][j] + '0'; 93 _for(k, 0, 11) 94 { 95 if(word[k] == '0' && j == 0) continue; 96 if(t == word[k]) 97 { 98 if(dfs2(ti, tj, d)) 99 return true; 100 } 101 else 102 { 103 if(k==0) 104 { 105 p[i][j] = -1; 106 if(dfs2(ti, tj, d + 1)) return true; 107 } 108 else 109 { 110 p[i][j] = word[k]-'0'; 111 if(dfs2(ti, tj, d + 1)) return true; 112 } 113 if(t=='*') 114 p[i][j] = -1; 115 else 116 p[i][j] = t-'0'; 117 } 118 } 119 return false; 120 } 121 122 void ID() 123 { 124 for(maxd=0; ; maxd ++) 125 if(dfs2(0,0,0)) return ; 126 } 127 128 int kase = 1; 129 void output() 130 { 131 printf("Case %d: ",kase++); 132 _for(i,0,3) 133 { 134 _for(j,0,p[i].size()) 135 { 136 if(p[i][j]==-1) 137 cout << '*'; 138 else 139 cout << p[i][j]; 140 } 141 if(i!=2) 142 cout << " "; 143 } 144 cout << endl; 145 } 146 147 int main() 148 { 149 string str; 150 while(getline(cin,str)&&str[0]!='0') 151 { 152 _for(i,0,3) 153 p[i].clear(); 154 int pEnd = 0; 155 _for(i,0,str.size()) 156 { 157 if(str[i]=='*') 158 p[pEnd].pb(-1); 159 else if(str[i]==' ') 160 pEnd ++; 161 else 162 p[pEnd].pb(str[i]-'0'); 163 } 164 ID(); 165 output(); 166 } 167 return 0; 168 }