POJ 1113 Wall 凸包面积 poj 2187 Beauty Contest

题目连接http://poj.org/problem?id=1113

1113

#include <stdio.h>
#include<algorithm>
#include <math.h>
using namespace std;

int q[50050];
int f;
struct node
{
    int x,y;
}a[50050];

int cmp(struct node p1,struct node p2)
{
    int x1 = p1.x-a[0].x;
    int x2 = p2.x-a[0].x;
    int y1 = p1.y-a[0].y;
    int y2 = p2.y-a[0].y;
    if(x1*y2 == x2*y1)
    return x1*x1+y1*y1 < x2*x2+y2*y2;
    return x1*y2 > x2*y1;
}

double dis(int i,int j)
{
    double x,y;
    x = a[i].x-a[j].x;
    y = a[i].y-a[j].y;
    return sqrt(x*x+y*y);
}
int is_left(int i,int j,int k)
{
    int x1 = a[j].x-a[i].x;
    int x2 = a[k].x-a[j].x;
    int y1 = a[j].y-a[i].y;
    int y2 = a[k].y-a[j].y;

    return x1*y2 >= x2*y1;
}
int main()
{
    int n,i,j,temp,r;
    while(~scanf("%d %d",&n,&r))
    {
        temp = 0;
        for(i = 0;i < n;i++)
        {
            scanf("%d %d",&a[i].x,&a[i].y);
            if(a[i].x > a[temp].x && a[temp].y <= a[i].y)
            temp =i;
        }
        if(i)
        {
            struct node t;
            t = a[temp];
            a[temp] = a[0];
            a[0] = t;
        }

        sort(a+1,a+n,cmp);

        f = 0;
        q[f++] = 0;
        q[f++] = 1;
        q[f++] = 2;

        for(i = 3;i < n;)
        {
            if(f < 2 || is_left(q[f-2],q[f-1],i))
            q[f++] = i++;
            else
            f--;
        }
        q[f] = q[0];
        double ans = 0;
        for(i = 0;i < f;i++)
        {
            ans += dis(q[i],q[i+1]);
        }
        ans += 2*r*3.141592653;
        printf("%.0f\n",ans);
    }
    return 0;
}

2187

#include <stdio.h>
#include<algorithm>

using namespace std;

int q[50050];
int f;
struct node
{
    int x,y;
}a[50050];
int cmp(node b,node c)
{
    int x1 = b.x-a[0].x;
    int x2 = c.x-a[0].x;
    int y1 = b.y-a[0].y;
    int y2 = c.y-a[0].y;
    if(x1*y2 == x2*y1)
    return x1*x1+y1*y1 < x2*x2+y2*y2;

    return x1*y2>x2*y1;
}
int is_left(int i,int j,int k)
{
    int x1 = a[j].x-a[i].x;
    int x2 = a[k].x-a[j].x;
    int y1 = a[j].y-a[i].y;
    int y2 = a[k].y-a[j].y;
    if(x1*y2>x2*y1)
    return 1;
    return 0;
}

int dis(int i,int j)
{
    return (a[j].x-a[i].x)*(a[j].x-a[i].x)+(a[j].y-a[i].y)*(a[j].y-a[i].y);
}
int main()
{
    int n,i,j,ans,temp;
    while(~scanf("%d",&n))
    {
        temp = 0;
        for(i = 0;i < n;i++)
        {
            scanf("%d %d",&a[i].x,&a[i].y);
            if(a[temp].x > a[i].x && a[temp].y >= a[i].y)
            temp = i;
        }

        if(temp)
        {
            struct node t;
            t = a[0];
            a[0] = a[temp];
            a[temp] = t;
        }
        sort(a+1,a+n,cmp);

        f = 0;

        q[f++] = 0;
        q[f++] = 1;
        q[f++] = 2;
        for(i = 3;i < n;)
        {
            if(f < 2||is_left(q[f-2],q[f-1],i))
            {
                q[f++] = i++;
            }
            else
            f--;
        }
        q[f] = q[0];
        ans = 0;
        for(i = 0;i < f;i++)
        {

            for(j = i+1;j < f;j++)
            if(ans < dis(q[i],q[j]))
            ans = dis(q[i],q[j]);
        }
        printf("%d\n",ans);
    }
    return 0;
}

#include <stdio.h>
#include <string.h>
#define N 5050
int dp[2][N];
int main()
{
    int n,i,j;

    char str[N];
    while(~scanf("%d",&n))
    {
        getchar();
        gets(str);
        memset(dp,0,sizeof(dp));
        for(i = n-1;i >= 0;i--)
        {
            for(j = i+1;j < n;j++)
            {
                if(str[i] == str[j])
                dp[i][j] = dp[(i+1)][j-1];
                else
                dp[i][j] = (dp[(i+1)][j] < dp[(i)][j-1]?dp[i+1][j]:dp[i][j-1])+1;
            }
        }
        printf("%d\n",dp[0][n-1]);
    }
    return 0;
}