# poj 2560 Freckles

## 题目连接

http://poj.org/problem?id=2560

# Freckles

## Description

In an episode of the Dick Van Dyke show, little Richie connects the freckles on his Dad‘s back to form a picture of the Liberty Bell. Alas, one of the freckles turns out to be a scar, so his Ripley‘s engagement falls through.
Consider Dick‘s back to be a plane with freckles at various (x,y) locations. Your job is to tell Richie how to connect the dots so as to minimize the amount of ink used. Richie connects the dots by drawing straight lines between pairs, possibly lifting the pen between lines. When Richie is done there must be a sequence of connected lines from any freckle to any other freckle.

## Input

The first line contains 0 < n <= 100, the number of freckles on Dick‘s back. For each freckle, a line follows; each following line contains two real numbers indicating the (x,y) coordinates of the freckle.

## Output

Your program prints a single real number to two decimal places: the minimum total length of ink lines that can connect all the freckles.

3
1.0 1.0
2.0 2.0
2.0 4.0

## Sample Output

3.41
\$n\$个点用\$Prim\$求最小生成树，开始用的\$double\$类型\$\%lf\$控制精度\$g++\$不停地wa后改为\$float，\%f\$过了/(ㄒoㄒ)/~~

```#include<algorithm>
#include<iostream>
#include<cstdlib>
#include<cstring>
#include<cstdio>
#include<vector>
#include<queue>
#include<cmath>
#include<set>
using std::set;
using std::pair;
using std::swap;
using std::multiset;
using std::priority_queue;
#define pb(e) push_back(e)
#define sz(c) (int)(c).size()
#define mp(a, b) make_pair(a, b)
#define all(c) (c).begin(), (c).end()
#define iter(c) __typeof((c).begin())
#define cls(arr, val) memset(arr, val, sizeof(arr))
#define cpresent(c, e) (find(all(c), (e)) != (c).end())
#define rep(i, n) for(int i = 0; i < (int)n; i++)
#define tr(c, i) for(iter(c) i = (c).begin(); i != (c).end(); ++i)
const int N = 110;
const int INF = 0x3f3f3f3f;
typedef unsigned long long ull;
struct P {
float x, y;
P(float i = 0.0, float j = 0.0) :x(i), y(j) {}
inline float calc(const P &k) const {
return sqrt((x - k.x) * (x - k.x) + (y - k.y) * (y - k.y));
}
}A[N];
struct PDI {
int v;
float s;
PDI(int i = 0, float j = 0.0) :v(i), s(j) {}
inline bool operator<(const PDI &k) const {
return s > k.s;
}
};
struct Prim {
bool vis[N];
float mincost[N];
struct edge { int to; float w; int next; }G[(N * N) << 1];
inline void init(int n) {
tot = 0;
rep(i, n + 1) {
vis[i] = false;
mincost[i] = INF;
}
}
inline void add_edge(int u, int v, float w) {
G[tot] = (edge){ v, w, head[u] }; head[u] = tot++;
}
inline void built(int n) {
rep(i, n) scanf("%f %f", &A[i].x, &A[i].y);
for (int i = 0; i < n; i++) {
for (int j = 0; j < n; j++) {
if (i == j) continue;
add_edge(i + 1, j + 1, A[i].calc(A[j]));
}
}
}
inline void prim(int s = 1) {
float ans = 0.0;
priority_queue<PDI> q;
q.push(PDI(s));
for (int i = head[s]; ~i; i = G[i].next) {
edge &e = G[i];
q.push(PDI(e.to, mincost[e.to] = e.w));
}
vis[s] = true;
while (!q.empty()) {
PDI t = q.top(); q.pop();
int u = t.v;
if (vis[u]) continue;
vis[u] = true;
ans += mincost[u];
for (int i = head[u]; ~i; i = G[i].next) {
edge &e = G[i];
if (mincost[e.to] > e.w && !vis[e.to]) {
q.push(PDI(e.to, mincost[e.to] = e.w));
}
}
}
printf("%.2f\n", ans);
}
inline void solve(int n) {
init(n), built(n), prim();
}
}go;
int main() {
#ifdef LOCAL
freopen("in.txt", "r", stdin);
freopen("out.txt", "w+", stdout);
#endif
int n;
while (~scanf("%d", &n)) {
go.solve(n);
}
return 0;
}```

## POJ 2560

1 #include<iostream> 2 #include<algorithm> 3 #include<cmath> 4 #include<iomanip> 5 #define MAXN 105 6 #define inf 1000000000 7 using namespace std; 8 9 typedef double elem_t; 10 11 double point[MAXN][2]; 12 double _m[MAXN][MAXN]; 1

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