pku3670 Eating Together

http://poj.org/problem?id=3670

DP，最长不降子序列，O(n*logn)解法

#include <stdio.h>
#define N 30030

int n, a[N], dp[N];
const int maxint = (1<<31)-1;

int bs(int l ,int r, int x)
{
    int m;
    while(l < r)
    {
        m = (l + r)>>1;
        if(dp[m] <= x)
        {
            l = m + 1;
        }
        else
        {
            r = m;
        }
    }
    return l;
}

int LIS()
{
    int i, j, maxn = 1;
    dp[0] = 0;
    dp[1] = maxint;
    for(i=1; i<=n; i++)
    {
        j = bs(0, maxn+1, a[i]);
        dp[j] = a[i];
        if(j > maxn)
        {
            maxn ++;
            dp[maxn+1] = maxint;
        }
    }
    return maxn;
}

int main()
{
    int t, i, j;
    int r1, r2;
    while(~scanf("%d", &n))
    {
        for(i=1; i<=n && scanf("%d", a+i); i++);
        r1 = LIS();
        for(i=1; i<=n/2; i++)
        {
            j = n-i+1;
            //printf("%d %d
", i, j);
            a[i] ^= a[j], a[j] ^= a[i], a[i] ^= a[j];
        }
        r2 = LIS();
        printf("%d
", n - (r1>r2? r1: r2));
    }
    return 0;
}