Orz AutSky_JadeK 他已经讲的很详细了，我只是个酱油233
1 /************************************************************** 2 Problem: 3754 3 User: rausen 4 Language: C++ 5 Result: Accepted 6 Time:9024 ms 7 Memory:892 kb 8 ****************************************************************/ 9 10 #include <cstdio> 11 #include <cmath> 12 #include <algorithm> 13 14 using namespace std; 15 typedef double lf; 16 const int N = 105; 17 const int M = 2005; 18 const int Maxlen = 30005; 19 20 struct edges { 21 int x, y, v; 22 lf w; 23 24 inline bool operator < (const edges &b) const { 25 return w < b.w; 26 } 27 } e[M]; 28 inline bool cmp_min(edges a, edges b) { 29 return a.v < b.v; 30 } 31 inline bool cmp_max(edges a, edges b) { 32 return a.v > b.v; 33 } 34 35 36 int n,m, Min, Max, fa[N]; 37 lf ans = (lf) 1e15; 38 39 char buf[Maxlen], *c = buf; 40 int Len; 41 42 inline int read() { 43 int x = 0; 44 while (*c < '0' || '9' < *c) ++c; 45 while ('0' <= *c && *c <= '9') 46 x = x * 10 + *c - '0', ++c; 47 return x; 48 } 49 50 lf Sqr(lf x) { 51 return x * x; 52 } 53 54 int find(int x) { 55 return x == fa[x] ? x : fa[x] = find(fa[x]); 56 } 57 58 void work(int sum) { 59 lf A = (lf) sum / (n - 1), res = 0; 60 int cost = 0, tot = 0, fa1, fa2, i; 61 for (i = 1; i <= n; ++i) 62 fa[i] = i; 63 for (i = 1; i <= m; ++i) 64 e[i].w = Sqr((lf) e[i].v - A); 65 sort(e + 1, e + m + 1); 66 for (i = 1; i <= m; ++i) 67 if ((fa1 = find(e[i].x)) != (fa2 = find(e[i].y))) { 68 fa[fa1] = fa2; 69 cost += e[i].v; 70 res += e[i].w; 71 if (++tot == n - 1) break; 72 } 73 if (cost == sum) 74 ans = min(ans, res); 75 } 76 77 int main() { 78 int i; 79 Len = fread(c, 1, Maxlen, stdin); 80 buf[Len] = ' '; 81 n = read(), m = read(); 82 for (i = 1; i <= m; ++i) 83 e[i].x = read(), e[i].y = read(), e[i].v = read(); 84 sort(e + 1, e + m + 1, cmp_min); 85 for (i = 1; i < n; ++i) 86 Min += e[i].v; 87 sort(e + 1, e + m + 1, cmp_max); 88 for (i = 1; i < n; ++i) 89 Max += e[i].v; 90 for (i = Min; i <= Max; ++i) 91 work(i); 92 printf("%.4lf ", sqrt((lf) ans / (n - 1))); 93 }
（p.s. 这输出样例是错的。。。对的应该是0.7071貌似= =）