預設是單調遞增：

#include<stdio.h>
#include<iostream>
#include<string.h>
#include<algorithm>
using namespace std;
int a[1000005];
char c[1000005];
int maxv[1000005];
int bin(int x,int len)
{
    int left,right,mid;
    left=1;
    right=len;
    while(left<=right)
    {
        mid=left+(right-left)/2;
        if(maxv[mid]==x)
            return mid;//(2)return mid+1;//非遞減
        else if(maxv[mid]<x)//(1)maxv[mid]>x:單調遞減
            left=mid+1;
        else
            right=mid-1;
    }
    return left;
}
int main()
{
    int n,i,j,len;
    scanf("%d",&n);
    while(n--)
    {
        scanf("%s",c);
        for(i=0; i<strlen(c); i++)
        {
            a[i+1]=c[i]-'a';
        }
        maxv[1]=a[1];
        len=1;
        for(i=2; i<=strlen(c); i++)
        {
            if(a[i]>maxv[len])//(1) <
                maxv[++len]=a[i];
            else
            {
                int pos=bin(a[i],len);
                maxv[pos]=a[i];
            }
        }
        printf("%d\n",len);
    }
}