POJ 3617 Best Cow Line（模拟+贪心）

待我称王封你为后i 2022-06-10 22:51 141阅读 0赞

FJ is about to take his *N* (1 ≤ *N* ≤ 30,000) cows to the annual"Farmer of the Year" competition. In this contest every farmer arranges his cows in a line and herds them past the judges.

The contest organizers adopted a new registration scheme this year: simply register the initial letter of every cow in the order they will appear (i.e., If FJ takes Bessie, Sylvia, and Dora in that order he just registers BSD). After the registration phase ends, every group is judged in increasing lexicographic order according to the string of the initials of the cows' names.

FJ is very busy this year and has to hurry back to his farm, so he wants to be judged as early as possible. He decides to rearrange his cows, who have already lined up, before registering them.

FJ marks a location for a new line of the competing cows. He then proceeds to marshal the cows from the old line to the new one by repeatedly sending either the first or last cow in the (remainder of the) original line to the end of the new line. When he's finished, FJ takes his cows for registration in this new order.

Given the initial order of his cows, determine the least lexicographic string of initials he can make this way.

Input

\* Line 1: A single integer: *N*  
\* Lines 2..*N*\+1: Line *i*\+1 contains a single initial ('A'..'Z') of the cow in the *i*th position in the original line

Output

The least lexicographic string he can make. Every line (except perhaps the last one) contains the initials of 80 cows ('A'..'Z') in the new line.

Sample Input

6
    A
    C
    D
    B
    C
    B

Sample Output

ABCBCD

题解：

一开始觉得很难。。后来发现水爆了的贪心，就是首尾比较，如果谁小取谁，如果一样比较下一位，取下一位小的，如果还一样继续，直到最后还一样就随便取，pe了一次原因是80位输出换行。。这么水不想写注释了qwq

代码：

#include<iostream>
    #include<stdio.h>
    #include<map>
    #include<algorithm>
    #include<math.h>
    #include<queue>
    #include<stack>
    #include<string>
    #include<cstring>
    using namespace std;
    int a[30005];
    int b[30005];
    int main()
    {
        int i,j,n,tot;
        char c;
        scanf("%d",&n);
        for(i=0;i<n;i++)
        {
            getchar();
            scanf("%c",&c);
            a[i]=c-'A';
        }
        int l=0,r=n-1,ans=0;
        while(ans<n)
        {
            if(a[l]<a[r])
            {
                b[ans]=a[l];
                l++;
            }
            else if(a[l]>a[r])
            {
                b[ans]=a[r];
                r--;
            }
            else
            {
                int ll=l,rr=r;
                while(a[ll]==a[rr]&&ll<=rr)
                {
                    ll++;
                    rr--;
                }
                if(ll>rr)
                {
                    b[ans]=a[l];
                    l++;
                }
                else
                {
                    if(a[ll]>a[rr])
                    {
                        b[ans]=a[r];
                        r--;
                    }
                    else
                    {
                        b[ans]=a[l];
                        l++;
                    }
                }
            }
            ans++;
        }
        for(i=0;i<n;i++)
        {
            printf("%c",'A'+b[i]);
            if((i+1)%80==0)
                printf("\n");
        }
        if((i+1)%80!=0)
            printf("\n");
        return 0;
    }