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[LeetCode] Regular Expression Matching

时间:2015-07-06 01:23:06      阅读:97      评论:0      收藏:0      [点我收藏+]

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This problem has a typical solution using Dynamic Programming. We define the state P[i][j] to be true if s[0..i) matches p[0..j) and false otherwise. Then the state equations are:

  1. P[i][j] = P[i - 1][j - 1], if p[j - 1] != ‘*‘ && (s[i - 1] == p[j - 1] || p[j - 1] == ‘.‘);
  2. P[i][j] = P[i][j - 2], if p[j - 1] == ‘*‘ and the pattern repeats for 0 times;
  3. P[i][j] = P[i - 1][j] && (s[i - 1] == p[j - 2] || p[j - 2] == ‘.‘), if p[j - 1] == ‘*‘ and the pattern repeats for at least 1 times.

Putting these together, we will have the following code.

 1 class Solution {
 2 public:
 3     bool isMatch(string s, string p) {
 4         int m = s.length(), n = p.length();
 5         vector<vector<bool> > dp(m + 1, vector<bool> (n + 1, false));
 6         dp[0][0] = true;
 7         for (int j = 1; j <= n; j++)
 8             dp[0][j] = (j > 1 && p[j - 1] == * && dp[0][j - 2]);
 9         for (int j = 1; j <= n; j++) {
10             for (int i = 1; i <= m; i++) {
11                 if (p[j - 1] == *) 
12                     dp[i][j] = dp[i][j - 2] || ((s[i - 1] == p[j - 2] || p[j - 2] == .) && dp[i - 1][j]);
13                 else dp[i][j] = dp[i - 1][j - 1] && (s[i - 1] == p[j - 1] || p[j - 1] == .);
14             }
15         }
16         return dp[m][n];
17     }
18 };

 

[LeetCode] Regular Expression Matching

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原文地址:http://www.cnblogs.com/jcliBlogger/p/4623211.html

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