HDU 1025 DP + 二分

题目：http://acm.hdu.edu.cn/showproblem.php?pid=1025
求最长递增子序列，O(n^2)的复杂度超时，需要优化为O(n*logn)
f[i]存储长度为i的最小末尾
#include<stdio.h>
int poor[500010], f[500010];
int main()
{
	int n, k = 1;
	while (scanf("%d", &n) != EOF)
	{
		int m, m1;
		for (int i = 0; i<n; i++)
		{
			scanf("%d%d", &m, &m1);
			poor[m] = m1;
		}
		f[1] = poor[1];
		int	length = 1;
		for (i = 2; i<=n; i++)
		{
			int low = 1;
			int high = length;
			while (low<=high)//二分
			{
				int mid = (low + high)/2;
				if (f[mid] < poor[i]) low = mid + 1;
				else high = mid - 1;
			}
			f[low] = poor[i];
			if (low > length) length ++;
		}
		
		printf("Case %d:
", k ++);
		if (length == 1)
			printf("My king, at most 1 road can be built.

");
		else
			printf("My king, at most %d roads can be built.

",length); 
	}
	return 0;
}