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10. regular expression matching 实现参考资料

admin 11月 14, 2020 0

Given an input string (s) and a pattern (p), implement regular expression matching with support for ‘.’ and ‘*‘.

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'.' Matches any single character.
'*' Matches zero or more of the preceding element.
The matching should cover the entire input string (not partial).

Note:

s could be empty and contains only lowercase letters a-z.

p could be empty and contains only lowercase letters a-z, and characters like . or *.

Example 1:

Input:
s = "aa"
p = "a"
Output: false
Explanation: "a" does not match the entire string "aa".

Example 2:

Input:
s = "aa"
p = "a*"
Output: true
Explanation: '*' means zero or more of the precedeng element, 'a'. Therefore, by repeating 'a' once, it becomes "aa".

Example 3:

Input:
s = "ab"
p = ".*"
Output: true
Explanation: ".*" means "zero or more (*) of any character (.)".

Example 4:

Input:
s = "aab"
p = "c*a*b"
Output: true
Explanation: c can be repeated 0 times, a can be repeated 1 time. Therefore it matches "aab".

Example 5:

Input:
s = "mississippi"
p = "mis*is*p*."
Output: false

正则匹配

实现

java

动态规划


   * 动态规划
   * @param s
   * @param p
   * @return
   */
  public boolean (String s, String p){
    if (s == null || p == null) {
      return false;
    }
    boolean[][] dp = new boolean[s.length()+1][p.length()+1];
    dp[0][0] = true;
    for (int i = 0; i < p.length(); i++) {
      if (p.charAt(i) == '*' && dp[0][i-1]) {
        dp[0][i+1] = true;
      }
    }
    for (int i = 0 ; i < s.length(); i++) {
      for (int j = 0; j < p.length(); j++) {
        if (p.charAt(j) == '.') {
          dp[i+1][j+1] = dp[i][j];
        }
        if (p.charAt(j) == s.charAt(i)) {
          dp[i+1][j+1] = dp[i][j];
        }
        if (p.charAt(j) == '*') {
          if (p.charAt(j-1) != s.charAt(i) && p.charAt(j-1) != '.') {
            dp[i+1][j+1] = dp[i+1][j-1];
          } else {
            dp[i+1][j+1] = (dp[i+1][j] || dp[i][j+1] || dp[i+1][j-1]);
          }
        }
      }
    }
    return dp[s.length()][p.length()];
  }

参考资料

regular-expression-matching