44-wildcard-matching.java

/*
44. Wildcard Matching
Hard - 30.7%

Given an input string (s) and a pattern (p), implement wildcard pattern matching with support for '?' and '*' where:
- '?' Matches any single character.
- '*' Matches any sequence of characters (including the empty sequence).

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

Example 1:
Input: s = "aa", p = "a"
Output: false
Explanation: "a" does not match the entire string "aa".

Example 2:
Input: s = "aa", p = "*"
Output: true
Explanation: '*' matches any sequence.

Example 3:
Input: s = "cb", p = "?a"
Output: false
Explanation: '?' matches 'c', but the second letter is 'a', which does not match 'b'.
*/

class Solution {
    public boolean isMatch(String s, String p) {
        int m = s.length(), n = p.length();
        boolean[][] dp = new boolean[m + 1][n + 1];
        
        // Base case: empty string matches empty pattern
        dp[0][0] = true;
        
        // Handle patterns like a* or *a* etc.
        for (int j = 1; j <= n; j++) {
            if (p.charAt(j - 1) == '*') {
                dp[0][j] = dp[0][j - 1];
            }
        }
        
        // Fill the DP table
        for (int i = 1; i <= m; i++) {
            for (int j = 1; j <= n; j++) {
                if (p.charAt(j - 1) == '*') {
                    // '*' can match empty sequence or any character
                    dp[i][j] = dp[i - 1][j] || dp[i][j - 1];
                } else if (p.charAt(j - 1) == '?' || s.charAt(i - 1) == p.charAt(j - 1)) {
                    // '?' matches any character, or exact character match
                    dp[i][j] = dp[i - 1][j - 1];
                }
                // else dp[i][j] remains false (no match)
            }
        }
        
        return dp[m][n];
    }
}