nyist_78_圈水池

#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <iostream>

using  namespace std;

const int N = 105;

struct point {
    long long x, y;
}p[N];

long long dis(point A, point B) {//两点距离 
    return (long long)sqrt((A.x - B.x) * (A.x - B.x) + (A.y - B.y) * (A.y - B.y));
}

long long crossProd(point A, point B, point C) {//叉乘 
    return (B.x - A.x) * (C.y - A.y) - (B.y - A.y) * (C.x - A.x);
}

int cmp1(const void *a, const void *b) {
    point *c = (point *)a;
    point *d = (point *)b;
    long long k = crossProd(p[0], *c, *d);
    if (k < 0 || (!k && dis(p[0], *c) > dis(p[0], *d))) return 1;
    return -1;
}

int cmp2(const void *a, const void *b) {
    point *c = (point *)a;
    point *d = (point *)b;
    if (c->x != d->x) return (int)(c->x - d->x);
    return (int)(c->y - d->y);
}

int Graham(point p[], int n) {//求凸包，返回凸包顶点个数 
    long long x = p[0].x;
    long long y = p[0].y;
    int mi = 0;
    for (int i=1; i<n; ++i) {
        if (p[i].y < y || (p[i].y == y && p[i].x < x)) {
            x = p[i].x;
            y = p[i].y;
            mi = i;
        }
    } 
    point tmp = p[0];
    p[0] = p[mi];
    p[mi] = tmp;
    qsort(p+1, n-1, sizeof(point), cmp1);

    int top = 1;
    for (int i=2; i<n; ++i) {
        while (crossProd(p[top-1], p[top], p[i]) <= 0 && top >= 1) --top;
        p[++top] = p[i];
    }
    return top + 1;
}

void solve(point p[], int n) {
    int top = Graham(p, n);
    qsort(p, top, sizeof(point), cmp2);
    for (int i=0; i<top; ++i) printf ("%lld %lld\n", p[i].x, p[i].y);
}

int main() {
    int t;
    scanf ("%d", &t);
    while (t--) {
        int n;
        scanf ("%d", &n);
        for (int i=0; i<n; ++i) scanf ("%lld%lld", &p[i].x, &p[i].y);
        solve(p, n);
    }
    return 0;
}