Regular Expression Matching (. and *)?

bool IsMatch(string s, string p)

return IsMatchHelper(s, p, 0, 0);

bool IsMatchHelper(string s, string p, int i, int j)

if (j == p.Length) return i == s.Length;

bool firstMatch = (i < s.Length) && (p[j] == s[i] || p[j] ==

'.');

if (j + 1 < p.Length && p[j + 1] == '*')

// Two cases:

// 1) Use zero occurrence of p[j] (skip)

// 2) If firstMatch, consume one char in s and keep pattern

at j

return IsMatchHelper(s, p, i, j + 2) ||

(firstMatch && IsMatchHelper(s, p, i + 1, j));

else

return firstMatch && IsMatchHelper(s, p, i + 1, j + 1);

Follow on:

Explanation:

Recursively matches strings supporting '.' (any char) and '*' (zero or more of preceding).