POJ 3903 Stock Exchange(LIS)

Stock Exchange

#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;

#define N 500005

int n;
int backup[N];
int a[N];
int top;

void LIS() {
    memset(backup, 0, sizeof(backup));

    top = 0;
    backup[top] = 0xbfbfbfbf;
    for(int i = 1; i <= n; i++) {
        //如果a[i]>栈顶部元素，则压栈
        if(a[i] > backup[top]) {
            backup[++top] = a[i];
        } else { //如果a[i]不大于栈顶部元素，则二分查找第一个比a[i]大的元素
            int l = 1, r = top;
            while(l <= r) {//二分找下标，下标从1开始
                int mid = (l+r) >> 1;
                if(a[i] > backup[mid])
                    l = mid + 1;
                else
                    r = mid - 1;
            }
            //替换a[i]
            backup[l] = a[i];
        }
    }
}

int main() {
    //freopen("data.in", "r", stdin);

    while(scanf("%d", &n) != EOF) {
        memset(a, 0, sizeof(a));

        for(int i = 1; i <= n; i++) {
            scanf("%d", &a[i]);
        }

        LIS();
        printf("%d\n", top);
    }

    return 0;
}