add: 0010

cpp/more/0010.cpp

@@ -0,0 +1,50 @@
+#include <string>
+#include <cstring>
+
+/**
+ * 10. Regular Expression Matching
+ *
+ * Given an input string s and a pattern p, implement regular expression matching with support for '.' and '*' where:
+ *
+ * '.' Matches any single character.
+ * '*' Matches zero or more of the preceding element.
+ * The matching should cover the entire input string (not partial).
+ */
+
+class Solution {
+private:
+    int dp[21][21];
+    int sl;
+
+    bool f(const char* s, const char* p, int sd = 0, int pd = 0) {
+        // Look at table
+        if (dp[sd][pd] >= 0)
+            return dp[sd][pd];
+        // Terminated regex?
+        if (!p[pd])
+            return dp[sd][pd] = !s[sd];
+        // Empty s?
+        if (!s[sd])
+            return dp[sd][pd] = (!p[pd]) || (p[pd + 1] == '*' && f(s, p, sd, pd + 2));
+        // Look ahead
+        if (p[pd + 1] != '*')
+            return dp[sd][pd] = (p[pd] == '.' || p[pd] == s[sd]) && f(s, p, sd + 1, pd + 1);
+        // Contains *
+        // Match 0 or all chars.
+        for (int nsd = sd; nsd <= this->sl;) {
+            if (f(s, p, nsd, pd + 2))
+                return dp[sd][pd] = true;
+            if (p[pd] != s[nsd++] && p[pd] != '.')
+                break;
+        }
+        return dp[sd][pd] = false;
+    }
+
+public:
+    bool isMatch(const std::string& s, const std::string& p) {
+        std::memset(this->dp, -1, sizeof this->dp);
+        this->sl = s.length();
+        return f(s.c_str(), p.c_str());
+    }
+};
+