Safecracker

问题陈述：

　　杭州电子科技大学HANGZHOU DIANZI UNIVERSITY Online Judge Problem - 1015

 

问题解析：

　　深度优先搜索(Depth_First Search)

 

代码详解：　　

 1 #include <iostream>

 2 #include <cstdio>

 3 #include <cstdlib>

 4 #include <cstring>

 5 

 6 using namespace std;

 7 

 8 int flag, visited[12];

 9 

10 int cmp(const void *a, const void *b){

11     return *(char *)b - *(char *)a;

12 }

13 

14 int calculate(char *ans) {

15     int res = 0, x = 1, sign = 1;

16     for(int i=0; i<5; i++) {

17         for(int j=0; j<=i; j++) {

18             x *= (ans[i] - 'A' + 1);

19         }

20         res += x * sign;

21         x = 1;

22         sign *= (-1);

23     }

24     return res;

25 }

26 

27 void dfs(char *str, int target, char *ans, int depth, int len) {

28     if(depth == 5) {

29         if(calculate(ans) == target)

30             flag = 1;

31         return;

32     }

33     for(int i=0; i<len; i++) {

34         if(!visited[i]) {

35             ans[depth] = str[i];

36             visited[i] = 1;

37             dfs(str, target, ans, depth+1, len);

38             if(flag)

39                 return;

40             visited[i] = 0;

41         }

42     }

43 }

44 

45 int main()

46 {

47     int target;

48     char ans[6], str[13];

49     while(scanf("%d %s", &target, str)!=EOF && !(target==0 && strcmp(str, "END")==0)) {

50         memset(visited, 0, sizeof(visited));

51         qsort(str, strlen(str), sizeof(char), cmp);

52         flag = 0;

53         dfs(str, target, ans, 0, strlen(str));

54         if(flag){

55             ans[5] = '\0';

56             puts(ans);

57         } else {

58             puts("no solution");

59         }

60     }

61     return 0;

62 }

 

参考博客：CSDN Kizuki 

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