URAL 1501. Sense of Beauty(记忆化搜索)

题目链接

本来暴力写个TLE了，加上记忆化就A了。

 1 #include <cstring>

 2 #include <cstdio>

 3 #include <string>

 4 #include <iostream>

 5 #include <algorithm>

 6 #include <cmath>

 7 using namespace std;

 8 int pre[1001][1001];

 9 int flag[1001][1001];

10 char s1[1001],s2[1001];

11 int sum1[1001],sum2[1001];

12 int n;

13 int que[3001];

14 int dfs(int x,int y)

15 {

16     if(x == n&&y == n)

17     return 1;

18     if(flag[x][y] == 2)

19     return 0;

20     else if(flag[x][y] == 1)

21     return 1;

22     if(x+1 <= n)

23     {

24         if(abs(sum1[x+1] + sum2[y]-(x+1+y-sum1[x+1]-sum2[y])) <= 1)

25         {

26             pre[x+1][y] = 1;

27             if(dfs(x+1,y))

28             return flag[x+1][y] = 1;

29             else

30             {

31                 flag[x+1][y] = 2;

32                 pre[x+1][y] = 0;

33             }

34         }

35     }

36     if(y+1 <= n)

37     {

38         if(abs(sum1[x] + sum2[y+1]-(x+y+1-sum1[x]-sum2[y+1])) <= 1)

39         {

40             pre[x][y+1] = 2;

41             if(dfs(x,y+1))

42             return flag[x][y+1] = 1;

43             else

44             {

45                 flag[x][y+1] = 2;

46                 pre[x][y+1] = 0;

47             }

48         }

49     }

50     return 0;

51 }

52 int main()

53 {

54     int i,x,y;

55     scanf("%d%s%s",&n,s1,s2);

56     if(s1[0] == '1')

57     sum1[1] = 1;

58     if(s2[0] == '1')

59     sum2[1] = 1;

60     for(i = 2;i <= n;i ++)

61     {

62         if(s1[i-1] == '1')

63         sum1[i] = sum1[i-1] + 1;

64         else

65         sum1[i] = sum1[i-1];

66         if(s2[i-1] == '1')

67         sum2[i] = sum2[i-1] + 1;

68         else

69         sum2[i] = sum2[i-1];

70     }

71     if(dfs(0,0))

72     {

73         x = n;

74         y = n;

75         int m = 0;

76         while(x != 0||y != 0)

77         {

78             que[m++] = pre[x][y];

79             if(pre[x][y] == 1)

80             x --;

81             else

82             y --;

83         }

84         for(i = m-1;i >= 0;i --)

85         printf("%d",que[i]);

86         printf("\n");

87     }

88     else

89     printf("Impossible\n");

90     return 0;

91 }