1626: [Usaco2007 Dec]Building Roads 修建道路 （生成树）

此题求距离时直接平方会爆int。

#include<algorithm>#include<iostream>#include<cstdio>#include<cmath>using namespace std;inline int read() {    int x = 0, f = 1;    char ch = getchar();    while (ch < '0' || ch > '9') {        if (ch == '-')f = -1;        ch = getchar();    }    while (ch >= '0' && ch <= '9') {        x = x * 10 + ch - '0';        ch = getchar();    }    return x*f;}struct edge {    int x, y;    double v;} e[1000001];int n, m, cnt, tot, x[1001], y[1001], fa[1001];bool mp[1001][1001];double ans;inline bool cmp(edge a, edge b) {    return a.v < b.v;}inline int find(int x) {    return fa[x] == x ? x : fa[x] = find(fa[x]);}inline long long sqr(int x) {    return (long long) x*x;}inline double dis(int a, int b) {    return sqrt(sqr(x[a] - x[b]) + sqr(y[a] - y[b]));}int main() {    n = read();    m = read();    for (int i = 1; i <= n; i++) {        fa[i] = i;        x[i] = read();        y[i] = read();    }    for (int i = 1; i <= m; i++) {        int a = find(read()), b = find(read());        fa[a] = b;    }    for (int i = 1; i < n; i++)        for (int j = i + 1; j <= n; j++) {            e[++cnt] = (edge){i, j, dis(i, j)};        }    sort(e + 1, e + cnt + 1, cmp);    for (int i = 1; i <= cnt; i++) {        int p = find(e[i].x), q = find(e[i].y);        if (p != q) {            fa[p] = q;            ans += e[i].v;            tot++;            if (tot == n - 1)break;        }    }    printf("%.2lf", ans);    return 0;}