hihoCoder#1139 二分·二分答案

原题地址

 

挺简单一道题，结果因为一时傻逼写错一个小地方，导致WA成狗了_(:з」∠)_

 

代码：

 1 #include <iostream>

 2 #include <cstring>

 3 #include <queue>

 4 

 5 using namespace std;

 6 

 7 #define MAX_V 10008

 8 #define MAX_E 200008

 9 

10 int N, M, K, T;

11 int f[MAX_V];

12 bool v[MAX_V];

13 int n[MAX_E];

14 int w[MAX_E];

15 int t[MAX_E];

16 int max_w = 1;;

17 int min_w = 1000000;

18 

19 bool check(int l) {

20   queue<pair<int, int> > q;

21   memset(v, 0, sizeof(v));

22   q.push(pair<int, int>(1, K));

23   while (!q.empty()) {

24     pair<int, int> p = q.front();

25     q.pop();

26     if (p.first == T && p.second >= 0)

27       return true;

28     if (p.second == 0 || v[p.first])

29       continue;

30     v[p.first] = true;

31     for (int i = f[p.first]; i != 0; i = n[i]) {

32       if (w[i] > l || v[t[i]])

33         continue;

34       q.push(pair<int, int>(t[i], p.second - 1));

35     }

36   }

37   return false;

38 }

39 

40 int find(int l, int r) {

41   int res = r;

42   while (l <= r) {

43     int m = (l + r) / 2;

44     if (check(m)) {

45       res = m;

46       r = m - 1;

47     }

48     else

49       l = m + 1;

50   }

51   return res;

52 }

53 

54 int main() {

55   memset(n, 0, sizeof(n));

56   scanf("%d%d%d%d", &N, &M, &K, &T);

57   for (int i = 0, j = 0; i < M; i++) {

58     int a, b, c;

59     scanf("%d%d%d", &a, &b, &c);

60     min_w = min(min_w, c);

61     max_w = max(max_w, c);

62     j++;

63     w[j] = c;

64     t[j] = b;

65     n[j] = f[a];

66     f[a] = j;

67     j++;

68     w[j] = c;

69     t[j] = a;

70     n[j] = f[b];

71     f[b] = j;

72   }

73   if (T == 1)

74     printf("0\n");

75   else

76     printf("%d\n", find(min_w, max_w));

77   return 0;

78 }