UVA 11988 Broken Keyboard (a.k.a. Beiju Text)

Posted 2020-09-30 韵祈

题目代号：UVA 11988

题目链接：https://uva.onlinejudge.org/index.php?option=com_onlinejudge&Itemid=8&page=show_problem&problem=3139

You’re typing a long text with a broken keyboard. Well it’s not so badly broken. The only problem
with the keyboard is that sometimes the “home” key or the “end” key gets automatically pressed
(internally).
You’re not aware of this issue, since you’re focusing on the text and did not even turn on the
monitor! After you finished typing, you can see a text on the screen (if you turn on the monitor).
In Chinese, we can call it Beiju. Your task is to find the Beiju text.

Input
There are several test cases. Each test case is a single line containing at least one and at most 100,000
letters, underscores and two special characters ‘[’ and ‘]’. ‘[’ means the “Home” key is pressed
internally, and ‘]’ means the “End” key is pressed internally. The input is terminated by end-of-file
(EOF).

Output
For each case, print the Beiju text on the screen.

Sample Input
This_is_a_[Beiju]_text
[[]][][]Happy_Birthday_to_Tsinghua_University

Sample Output
BeijuThis_is_a__text
Happy_Birthday_to_Tsinghua_University

题目大意：‘[‘出现相当于跳到开头输入，‘]‘相当于跳到结尾，然后输出最终应该显示的模样。

解题思路：链表，但是链表太过于繁琐，不太方便，所以用数组模拟链表进行操作，详细参照算法竞赛与入门经典第二版，方法很巧妙，但是有点难理解，手动模拟一次操作然后思考一下就懂了。

代码：

# include <stdio.h>
# include <string.h>
# include <stdlib.h>
# include <iostream>
# include <fstream>
# include <vector>
# include <queue>
# include <stack>
# include <map>
# include <math.h>
# include <algorithm>
using namespace std;
# define pi acos(-1.0)
# define mem(a,b) memset(a,b,sizeof(a))
# define FOR(i,a,n) for(int i=a; i<=n; ++i)
# define For(i,n,a) for(int i=n; i>=a; --i)
# define FO(i,a,n) for(int i=a; i<n; ++i)
# define Fo(i,n,a) for(int i=n; i>a ;--i)
typedef long long LL;
typedef unsigned long long ULL;

const int MAXM=100005;
char s[MAXM];
int Next[MAXM];

int main()
{
    //freopen("in.txt", "r", stdin);
    int cur,last;//cur为光标位置，last为显示屏最后一个字符
    while(~scanf("%s",s+1))
    {
        memset(Next,0,sizeof(Next));
        int len = strlen(s+1);
        Next[0] = 0;
        cur = last = 0;
        for(int i = 1; i <= len; i++)
        {
            if(s[i] == ‘[‘)
                cur = 0;
            else if(s[i] == ‘]‘)
                cur = last;
            else
            {
                //模拟插入链表过程
                Next[i] = Next[cur];//第i个字符指向光标位置
                Next[cur] = i;//光标指向下一个字符
                if(cur == last)//只有光标在当前最后一个字符位置或是遇到]后才执行
                    last = i;
                cur = i;//移动光标
            }
        }
        for(int i = Next[0]; i != 0; i = Next[i])
            printf("%c",s[i]);
        printf("\n");
        memset(s,0,sizeof(s));
    }
    return 0;
}