Vijos 1012 清帝之惑之雍正

1.暴力

//按x第一关键词，按y第二关键词排，这样当if(a[j].x - a[i].x >= ans)时，后面的j一定不会比已有ans更优秀，疯狂剪枝。#include<bits/stdc++.h>using namespace std;int n;const int maxn = 100010;double ans = 0x7fffffff;struct node{    int x, y;} a[maxn];bool cmp(node p, node q){    if(p.x == q.x)  return p.y < q.y;    return p.x < q.x;}int main(){    cin >> n;    for(int i = 1; i <= n; i++){        cin >> a[i].x >> a[i].y;        /*maxx = max(a[i].x, maxx);        maxy = max(a[i].y, maxy);*/    }    sort(a+1, a+n+1, cmp);    for(int i = 1; i <= n; i++)        for(int j = i+1; j <= n; j++){            if(a[j].x - a[i].x >= ans)  break;             double now = sqrt(pow(a[i].x - a[j].x, 2) + pow(a[i].y - a[j].y, 2));            ans = min(now, ans);        }    printf("%.3lf\n", ans);    return 0;}

2.分治

//切记sqrt()中要加(double)!!!!! //3 1113333 223332 33333333 333333 23 23#include<bits/stdc++.h>using namespace std;int n;const int maxn = 100010;const int inf = 0x3f3f3f3f;struct node{    int x, y;} a[maxn], t[maxn];bool cmp(node p, node q){    if(p.x != q.x)  return p.x < q.x;    return p.y < q.y;}bool cmpy(node p, node q){    return p.y < q.y;}double dis(node p, node q){    return sqrt((double)(p.x - q.x)*(p.x - q.x) + (double)(p.y - q.y)*(p.y - q.y));}double changsort(int x, int y){    double ans = 0x3fffffff;    if(y - x == 1)  return inf;    if(y - x == 2)  return dis(a[x], a[x+1]);    int m = x + (y-x)/2;    double d1 = changsort(x, m);    double d2 = changsort(m, y);    ans = min(d1, d2);    int cnt = 0;    for(int i = x; i <= m; i++)        if(fabs(a[i].x - a[m].x) < ans){            t[++cnt].x = a[i].x;            t[cnt].y = a[i].y;        }    sort(t+1, t+cnt+1, cmpy);    for(int i = 1; i <= cnt; i++)        for(int j = i+1; j <= cnt && abs(t[i].y - t[j].y) < ans; j++){            double d3 = dis(t[i], t[j]);            ans = min(ans, d3);        }    return ans;}int main(){    cin >> n;    for(int i = 1; i <= n; i++){        cin >> a[i].x >> a[i].y;        /*maxx = max(a[i].x, maxx);        maxy = max(a[i].y, maxy);*/    }    sort(a+1, a+n+1, cmp);    printf("%.3lf\n", changsort(1, n+1));    return 0;}