[洛谷P1265]公路修建
题目传送门
这道题是稠密图，要用$Prim$，可以对照P1991的$Kruskal$，但在这里用会$MLE$会$TLE$。
1 #include <bits/stdc++.h> 2 3 using namespace std; 4 5 #define re register 6 #define rep(i, a, b) for (re int i = a; i <= b; ++i) 7 #define repd(i, a, b) for (re int i = a; i >= b; --i) 8 #define maxx(a, b) a = max(a, b); 9 #define minn(a, b) a = min(a, b); 10 #define LL long long 11 #define INF (1 << 30) 12 13 inline int read() { 14 int w = 0, f = 1; char c = getchar(); 15 while (!isdigit(c)) f = c == '-' ? -1 : f, c = getchar(); 16 while (isdigit(c)) w = (w << 3) + (w << 1) + (c ^ '0'), c = getchar(); 17 return w * f; 18 } 19 20 const int maxn = 5000 + 5; 21 22 LL sqr(LL x) { return x * x; } 23 double dist(int x1, int y1, int x2, int y2) { return sqrt(sqr(x1-x2) + sqr(y1-y2)); } 24 25 int n, x[maxn], y[maxn], v[maxn]; 26 double ans = 0, t[maxn]; 27 28 int main() { 29 n = read(); 30 31 rep(i, 1, n) x[i] = read(), y[i] = read(); 32 33 memset(v, 0, sizeof(v)); 34 int p = 1; 35 v[p] = 1; 36 rep(i, 1, n) t[i] = INF; 37 rep(kase, 1, n-1) { 38 int _min = 0; 39 rep(i, 1, n) 40 if (!v[i]) { 41 minn(t[i], dist(x[p], y[p], x[i], y[i])); 42 if (!_min || t[i] < t[_min]) _min = i; 43 } 44 ans += t[_min]; 45 v[_min] = 1; 46 p = _min; 47 } 48 49 printf("%.2lf", ans); 50 51 return 0; 52 }
