51nod 1134 最长递增子序列

题目链接：51nod 1134 最长递增子序列

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
const int N = 50001;
int a[N];
int b[N];
int Search(int num, int low, int high){
    int mid;
    while(low <= high){
        mid = (low + high)/2;
        if(num >= b[mid]) low = mid + 1;
        else high = mid - 1;
    }
    return low;
}
int DP(int n){
    int i, len, pos;
    b[1] = a[1];
    len = 1;
    for(i = 2; i <= n; i++){
        if(a[i] >= b[len])
            b[++len] = a[i];
        else{
            pos = Search(a[i],1,len);
            //在b[]数组中找出第一个比a[i]大的位置并且让a[i]替代这个位置
            b[pos] = a[i];
        }
    }
    return len;
}
int main(){
    int n, i, j;
    scanf("%d", &n);
    for(i = 1; i <= n; ++i)
        scanf("%d", &a[i]);
    int len = DP(n);
    printf("%d\n", len);
    return 0;
}