LeetCode 010-Regular Expression Matching

最新推荐文章于 2023-02-11 13:26:38 发布

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本文介绍了一种实现正则表达式匹配的方法，重点讲解了如何处理‘.’和‘*’这两个特殊字符，并通过递归的方式实现了字符串与模式的完全匹配。文章提供了详细的代码示例并解释了各种特殊情况的处理方式。

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Implement regular expression matching with support for '.' and '*'.

'.' Matches any single character.
'*' Matches zero or more of the preceding element.

The matching should cover the entire input string (not partial).

The function prototype should be:
bool isMatch(const char *s, const char *p)

Some examples:
isMatch("aa","a") → false
isMatch("aa","aa") → true
isMatch("aaa","aa") → false
isMatch("aa", "a*") → true
isMatch("aa", ".*") → true
isMatch("ab", ".*") → true
isMatch("aab", "c*a*b") → true

难度：难

代码：该题要理清思路从p的length入手，分情况讨论

public class Solution {
    public boolean isMatch(String s, String p) {
<span style="white-space:pre">		</span>if (p.length() == 0)
<span style="white-space:pre">			</span>return s.length() == 0;


<span style="white-space:pre">		</span>if (s.length() == 0) {
<span style="white-space:pre">			</span>if (p.length() == 1)
<span style="white-space:pre">				</span>return false;
<span style="white-space:pre">			</span>if (p.charAt(1) == '*')
<span style="white-space:pre">				</span>return isMatch(s, p.substring(2));
<span style="white-space:pre">			</span>return false;
<span style="white-space:pre">		</span>}


<span style="white-space:pre">		</span>if (p.length() == 1) {
<span style="white-space:pre">			</span>if (p.charAt(0) == '.' && s.length() == 1)
<span style="white-space:pre">				</span>return true;
<span style="white-space:pre">			</span>return s.equals(p);
<span style="white-space:pre">		</span>}


<span style="white-space:pre">		</span>if (p.length() >= 2 && p.charAt(1) != '*') {
<span style="white-space:pre">			</span>// if p(1) is not *, we need p(0) equals to s(0) or p(0) equals '.'
<span style="white-space:pre">			</span>if (p.charAt(0) == s.charAt(0) || p.charAt(0) == '.'
<span style="white-space:pre">					</span>&& s.length() != 0)
<span style="white-space:pre">				</span>// check if the left is also match
<span style="white-space:pre">				</span>return isMatch(s.substring(1), p.substring(1));
<span style="white-space:pre">			</span>return false;
<span style="white-space:pre">		</span>} else {
<span style="white-space:pre">			</span>while (s.length() > 0
                && (p.charAt(0) == s.charAt(0) || p.charAt(0) == '.')) {
            if (isMatch(s, p.substring(2)))
                return true;
            s = s.substring(1);
        }
        return isMatch(s, p.substring(2));}
<span style="white-space:pre">	</span>}
}