hdoj 1025 Constructing Roads In JGShining's Kingdom(最长上升子序列+二分）

题目：http://acm.hdu.edu.cn/showproblem.php?pid=1025

#include <iostream>
#include<cstdio>
#include<cstring>
#define maxn 500010
using namespace std;
int a[maxn];
int b[maxn];//存储序列长度为len的第i小的数中最小的数
int dp[maxn];
int chazhao(int x,int l,int r)//查找第i-1的长度序列中，结尾比a[i]小的最大长度
{
    int mid;
    while(l<=r)
    {
        mid=(l+r)/2;
        if(b[mid]<=x)
        l=mid+1;
        else
        r=mid-1;
    }
    return r;
}
int main()
{
    int x,y,i,n,k=0,len;
    while(scanf("%d",&n)!=EOF)
    {
        k++;
        for(i=0;i<n;i++)
        {
            scanf("%d%d",&x,&y);
            a[x]=y;
        }
        memset(b,-1,sizeof(b));
        dp[1]=1;
        b[1]=a[1];
        len=1;
        for(i=2;i<=n;i++)
        {
            int max=chazhao(a[i],1,len);
            dp[i]=max+1;
            if(b[i]==-1||b[dp[i]]>a[i])//更新b
            b[dp[i]]=a[i];
            if(len<dp[i])
            len=dp[i];
        }
        if(len==1)
        {
            printf("Case %d:\n",k);
        printf("My king, at most %d road can be built.\n\n",len);
        }
        else
        {
              printf("Case %d:\n",k);
        printf("My king, at most %d roads can be built.\n\n",len);
        }

    }
    return 0;
}