POJ2955Brackets[区间DP]
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Time Limit: 1000MS | Memory Limit: 65536K | |
Total Submissions: 6585 | Accepted: 3534 |
Description
We give the following inductive definition of a “regular brackets” sequence:
- the empty sequence is a regular brackets sequence,
- if s is a regular brackets sequence, then (s) and [s] are regular brackets sequences, and
- if a and b are regular brackets sequences, then ab is a regular brackets sequence.
- no other sequence is a regular brackets sequence
For instance, all of the following character sequences are regular brackets sequences:
(), [], (()), ()[], ()[()]
while the following character sequences are not:
(, ], )(, ([)], ([(]
Given a brackets sequence of characters a1a2 … an, your goal is to find the length of the longest regular brackets sequence that is a subsequence of s. That is, you wish to find the largest m such that for indices i1, i2, …, im where 1 ≤ i1 < i2 < … < im ≤ n, ai1ai2 … aim is a regular brackets sequence.
Given the initial sequence ([([]])]
, the longest regular brackets subsequence is [([])]
.
Input
The input test file will contain multiple test cases. Each input test case consists of a single line containing only the characters (
, )
, [
, and ]
; each input test will have length between 1 and 100, inclusive. The end-of-file is marked by a line containing the word “end” and should not be processed.
Output
For each input case, the program should print the length of the longest possible regular brackets subsequence on a single line.
Sample Input
((())) ()()() ([]]) )[)( ([][][) end
Sample Output
6 6 4 0 6
Source
题意:求最大括号匹配
f[i][j]表示i到j的最大括号匹配
#include<iostream> #include<cstdio> #include<algorithm> #include<cstring> using namespace std; const int N=105; char s[N]; int f[N][N]; inline bool check(int i,int j){ if(s[i]==‘[‘&&s[j]==‘]‘) return 1; if(s[i]==‘(‘&&s[j]==‘)‘) return 1; return 0; } int main(){ while(~scanf("%s",s+1)){ if(s[1]==‘e‘) break; memset(f,0,sizeof(f)); int n=strlen(s+1); for(int i=n;i>=1;i--) for(int j=i+1;j<=n;j++){ if(check(i,j)) f[i][j]=f[i+1][j-1]+2; for(int k=i;k<=j;k++) f[i][j]=max(f[i][j],f[i][k]+f[k][j]); } printf("%d\n",f[1][n]); } }
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