Sequence Decoding
题目描述
The amino acids in proteins are classified into two types of elements, hydrophobic (nonpolar) and hydrophilic (polar). Hydrophobic and hydrophilic are denoted by H and P respectively. A protein is represented by a sequence of H and P such as PPHHHPHPH. In order to reduce the representation length of a sequence, we use the notation k[S] to denote the repeated sequence of k times sequence S,where 2 ≤ k ≤ 9. A legal sequence is defined as following.
·A sequence consists of only one character ‘H’ or ‘P’ is a legal sequence.
·Let S1 and S2 be legal sequences. Then the sequence concatenated by S1 and S2 is also a legal sequence.
·Let S be a legal sequence. Then the sequence k[S] is also a legal sequence, where 2 ≤ k ≤ 9.
For example, PHPHPHPH is encoded as 4[PH]. Note that a repeated sequence may contains repeated sequences recursively such as 2[PH4[P]4[H]].
Given a nonempty encoded protein sequence S, your job is to expand S to its original sequence.
That is, you should expand 2[PH4[P]4[H]] to PHPPPPHHHHPHPPPPHHHH.
·A sequence consists of only one character ‘H’ or ‘P’ is a legal sequence.
·Let S1 and S2 be legal sequences. Then the sequence concatenated by S1 and S2 is also a legal sequence.
·Let S be a legal sequence. Then the sequence k[S] is also a legal sequence, where 2 ≤ k ≤ 9.
For example, PHPHPHPH is encoded as 4[PH]. Note that a repeated sequence may contains repeated sequences recursively such as 2[PH4[P]4[H]].
Given a nonempty encoded protein sequence S, your job is to expand S to its original sequence.
That is, you should expand 2[PH4[P]4[H]] to PHPPPPHHHHPHPPPPHHHH.
输入
The first line is an integer n indicating the number of test cases. Each of the next n lines consists of a legal sequence composed by number digits ‘2’~’9’, ‘[’, ‘]’, ‘P’ and ‘H’.
输出
For each test case, output the expanding sequence in one line.
样例输入
3
PHPHP
2[3[P]H2[P]]
HH2[P3[H]]P
样例输出
PHPHP
PPPHPPPPPHPP
HHPHHHPHHHP
提示
·1 ≤ n ≤ 10.
·All the inputs are legal.
·The length of each input sequence is less than 50.
·The length of each expanded sequence is less than 1000.
【题解】:
一开始想着怎么用栈来模拟,后来写不出来,队友提示用dfs写就好了。
我就用dfs写了。
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
1 #include<bits/stdc++.h> 2 using namespace std; 3 const int N = 1e5+10; 4 char s[N]; 5 int a[N],n,T; 6 void dfs( int L , int R ){ 7 int num = 0 ; 8 for( int i = L ; i <= R ;i ++ ){ 9 if( s[i] == 'P' || s[i] == 'H' ){ 10 printf("%c",s[i] ); 11 }else if( isdigit(s[i]) ){ 12 int j = i ; 13 num = 0 ; 14 while( isdigit(s[j]) && j < n ){ 15 num = num * 10 + s[i] - '0' ; 16 j ++ ; 17 } 18 i = j - 1 ; 19 }else if( s[i] == '[' ){ 20 for( int j = 0 ; j < num ; j++ ) 21 dfs( i+1 , a[i] - 1 ); 22 num = 1 ; 23 i = a[i] ; 24 }else if( s[i] == ']' ){ 25 continue ; 26 } 27 } 28 } 29 30 int main() 31 { 32 ios_base :: sync_with_stdio(false); 33 cin.tie(NULL) , cout.tie(NULL) ; 34 cin >> T ; 35 36 while(T--){ 37 cin >> s; 38 n = strlen( s ); 39 stack<int> st; 40 for( int i = 0 ; i < n ; i++ ){ 41 if( s[i] == '[' ){ 42 st.push(i) ; 43 }else if( s[i] == ']' ){ 44 int cur = st.top() ; 45 a[cur] = i ; 46 st.pop(); 47 } 48 } 49 dfs( 0 , n-1 ); 50 puts("") ; 51 } 52 return 0; 53 }