Update solutions to Regular Expression Matching and Wildcard Matching

Author: soapyigu

DP/RegularExpressionMatching.swift

@@ -6,31 +6,29 @@
 
 class RegularExpressionMatching {
     func isMatch(_ s: String, _ p: String) -> Bool {
-        let sChars = Array(s), pChars = Array(p)
-        var dp = Array(repeating: Array(repeating: false, count: pChars.count + 1), count: sChars.count + 1)
-        dp[0][0] = true
+        let s = Array(s), p = Array(p), m = s.count, n = p.count
+        var dp = Array(repeating: Array(repeating: false, count: n + 1), count: m + 1)
 
-        for i in 0...pChars.count {
-        	// jump over "" vs. "x*" case
-            dp[0][i] = i == 0 || i > 1 && dp[0][i - 2] && pChars[i - 1] == "*"
+        for j in 0...n {
+            dp[0][j] = j == 0 || (j > 1 && dp[0][j - 2] && p[j - 1] == "*") 
         }
 
-        for i in 0...sChars.count {
-            for j in 0...pChars.count {
-                guard j > 0 else {
-                    continue
-                }
-                
-                let pCurrent = pChars[j - 1]
-                
-                if pCurrent != "*" {
-                    dp[i][j] = i > 0 && dp[i - 1][j - 1] && (pCurrent == "." || pCurrent == sChars[i - 1])
+        for i in 1...m {
+            for j in 1...n {
+                if p[j - 1] != "*" {
+                    if p[j - 1] == s[i - 1] || p[j - 1] == "." {
+                        dp[i][j] = dp[i - 1][j - 1]
+                    } else {
+                        dp[i][j] = false
+                    }      
                 } else {
-                    dp[i][j] = dp[i][j - 2] || i > 0 && j > 1 && (sChars[i - 1] == pChars[j - 2] || pChars[j - 2] == ".") && dp[i - 1][j]
+                    if j > 1 {
+                        dp[i][j] = dp[i][j - 2] || ((p[j - 2] == s[i - 1] || p[j - 2] == ".") && dp[i - 1][j])
+                    }  
                 }
             }
         }
 
-        return dp[sChars.count][pChars.count]
+        return dp[m][n]
     }
 }

DP/WildcardMatching.swift

@@ -6,39 +6,31 @@
 
  class WildcardMatching {
     func isMatch(_ s: String, _ p: String) -> Bool {
-        let sChars = Array(s), pChars = Array(p)
-        var dp = Array(repeating: Array(repeating: false, count: p.count + 1), count: s.count + 1)
-        dp[0][0] = true
+        let s = Array(s), p = Array(p), m = s.count, n = p.count
+        var dp = Array(repeating: Array(repeating: false, count: n + 1), count: m + 1)
 
-        // must start from 0, to make range feasible and handle empty vs. * case
-        for i in 0...s.count {
-            for j in 0...p.count {
-                guard j > 0 else {
-                    continue
-                }
-                
-                let pCurrent = pChars[j - 1]
-    
-                if pCurrent != "*" {
-                    dp[i][j] = i > 0 && dp[i - 1][j - 1] && (pCurrent == sChars[i - 1] || pCurrent == "?")
-                } else {
-                	// Two situations:
-                    // (1) '*' is the first character in p;
-                    // (2) For k>=0 and k<=i, there is some dp[k][j-1] being true;
-                    //     and '*' will match the rest sequence in s after index k;
-                    var flag = false
-                    for k in 0...i {
-                        if dp[k][j - 1] {
-                            flag = true
-                            break
-                        }
+        for j in 0...n {
+            dp[0][j] = j == 0 || (dp[0][j - 1] && p[j - 1] == "*")
+        }
+        
+        if m < 1 || n < 1 {
+            return dp[m][n]
+        }
+        
+        for i in 1...m {
+            for j in 1...n {
+                if p[j - 1] != "*" {
+                    if p[j - 1] == s[i - 1] || p[j - 1] == "?" {
+                        dp[i][j] = dp[i - 1][j - 1]
+                    } else {
+                        dp[i][j] = false
                     }
-                    
-                    dp[i][j] = flag || j == 1   
+                } else {
+                    dp[i][j] = dp[i][j - 1] || dp[i - 1][j]
                 }
             }
         }
 
-        return dp[s.count][p.count]
+        return dp[m][n]
     }
 }