Ural 1654 Cipher Message
1654. Cipher Message
Time limit: 1.0 second
Memory limit: 64 MB
Müller tried to catch Stierlitz red-handed many times, but always failed because Stierlitz could ever find some excuse. Once Stierlitz was looking through his email messages. At that moment, Müller entered secretly and watched a meaningless sequence of symbols appear on the screen. “A cipher message,” Müller thought. “UTF-8,” Stierlitz thought
It is known that Stierlitz ciphers messages by the following method.
He deletes all spaces and punctuation marks.
He replaces all successive identical letters by one such letter.
He inserts two identical letters at an arbitrary place many times.
Try to restore a message as it was after the second step. For that, remove from the message all pairs of identical letters inserted at the third step.
Input
The only input line contains a message ciphered by Stierlitz. The message consists of lowercase English letters and its length is at most 200000.
Output
Output the restored message.
题意：
把一个序列中相邻的且是偶数个相同的字符删除，奇数个的话就只保留一个。但是要注意，删除的过程中，可能会导致本来不相邻的相同字符变得相邻了，这时候也要删除。
Solution:
用栈模拟，同为水题
代码：
#include<bits/stdc++.h> using namespace std; const int maxn=5000005; int len,top=0; char s[maxn]; inline int read() { int s=0,f=1; char c=getchar(); while (c<'0'||c>'9') { if (c=='-') { f=-1; } c=getchar(); } while (c>='0'&&c<='9') { s=s*10+c-48; c=getchar(); } return s*f; } int main() { while (scanf("%c",&s[top])!=EOF) { if (s[top]=='\n') { break; } if (top>0&&s[top]==s[top-1]) { top--; } else { top++; } } for (int i=0;i<=top;i++) { cout<<s[i]; } return 0; } /* wwstdaadierfflitzz */