modify leetcode problem 10 Regular Expression Matching

Author: 左程云

src/topinterviewquestions/Problem_0010_RegularExpressionMatching.java

@@ -49,6 +49,7 @@ public static boolean process(char[] str, char[] pattern, int si, int pi) {
 		if (pattern[pi] != '.' && str[si] != pattern[pi]) {
 			return process(str, pattern, si, pi + 2);
 		}
+		// si 没越界 pi 没越界 pi+1 * [pi]可配[si]
 		if (process(str, pattern, si, pi + 2)) {
 			return true;
 		}

src/topinterviewquestions/Problem_0010_RegularExpressionMatching2.java

@@ -0,0 +1,118 @@
+package topinterviewquestions;
+
+// Regular Expression Matching问题，进一步做斜率优化，把枚举行为优化掉
+
+public class Problem_0010_RegularExpressionMatching2 {
+
+	public static boolean isValid(char[] str, char[] pattern) {
+		for (char cha : str) {
+			if (cha == '.' || cha == '*') {
+				return false;
+			}
+		}
+		for (int i = 0; i < pattern.length; i++) {
+			if (pattern[i] == '*' && (i == 0 || pattern[i - 1] == '*')) {
+				return false;
+			}
+		}
+		return true;
+	}
+
+	public static boolean isMatch1(String s, String p) {
+		if (s == null || p == null) {
+			return false;
+		}
+		char[] str = s.toCharArray();
+		char[] pattern = p.toCharArray();
+		return isValid(str, pattern) && process(str, pattern, 0, 0);
+	}
+
+	public static boolean process(char[] str, char[] pattern, int si, int pi) {
+		if (si == str.length) { // si越界了
+			if (pi == pattern.length) {
+				return true;
+			}
+			if (pi + 1 < pattern.length && pattern[pi + 1] == '*') {
+				return process(str, pattern, si, pi + 2);
+			}
+			return false;
+		}
+		// si 没越界
+		if (pi == pattern.length) {
+			return si == str.length;
+		}
+		// si 没越界 pi 没越界
+		if (pi + 1 >= pattern.length || pattern[pi + 1] != '*') {
+			return ((str[si] == pattern[pi]) || (pattern[pi] == '.')) && process(str, pattern, si + 1, pi + 1);
+		}
+		// si 没越界 pi 没越界 pi+1 *
+		if (pattern[pi] != '.' && str[si] != pattern[pi]) {
+			return process(str, pattern, si, pi + 2);
+		}
+		if (process(str, pattern, si, pi + 2)) {
+			return true;
+		}
+		if (si + 1 >= str.length || str[si] != str[si + 1] && (pattern[pi] != '.')) {
+			return process(str, pattern, si + 1, pi + 2);
+		}
+		if (process(str, pattern, si + 1, pi)) {
+			return true;
+		}
+		return false;
+	}
+
+	public static boolean isMatch2(String s, String exp) {
+		if (s == null || exp == null) {
+			return false;
+		}
+		char[] str = s.toCharArray();
+		char[] pattern = exp.toCharArray();
+		if (!isValid(str, pattern)) {
+			return false;
+		}
+		boolean[][] dp = initDPMap(str, pattern);
+		for (int si = str.length - 1; si >= 0; si--) {
+			for (int pi = pattern.length - 2; pi >= 0; pi--) {
+				if (pattern[pi + 1] != '*') {
+					dp[si][pi] = ((str[si] == pattern[pi]) || (pattern[pi] == '.')) && dp[si + 1][pi + 1];
+				} else {
+					if (pattern[pi] != '.' && str[si] != pattern[pi]) {
+						dp[si][pi] = dp[si][pi + 2];
+					} else {
+						if (dp[si][pi + 2]) {
+							dp[si][pi] = dp[si][pi + 2];
+						} else {
+							if (si + 1 >= str.length || str[si] != str[si + 1] && (pattern[pi] != '.')) {
+								dp[si][pi] = dp[si + 1][pi + 2];
+							} else {
+								dp[si][pi] = dp[si + 1][pi];
+							}
+						}
+					}
+				}
+			}
+		}
+		return dp[0][0];
+	}
+
+	public static boolean[][] initDPMap(char[] s, char[] e) {
+		int slen = s.length;
+		int elen = e.length;
+		boolean[][] dp = new boolean[slen + 1][elen + 1];
+		dp[slen][elen] = true;
+		for (int j = elen - 2; j > -1; j = j - 2) {
+			if (e[j] != '*' && e[j + 1] == '*') {
+				dp[slen][j] = true;
+			} else {
+				break;
+			}
+		}
+		if (slen > 0 && elen > 0) {
+			if ((e[elen - 1] == '.' || s[slen - 1] == e[elen - 1])) {
+				dp[slen - 1][elen - 1] = true;
+			}
+		}
+		return dp;
+	}
+
+}