劍指Offer-16-正則表達式匹配

/**
 * 正則表達式匹配
 * @Description
 */
public class Test17 {
    //一行代碼
    public boolean isMatch1(String s, String p) {
        return s.matches(p);
    }

    //動態規劃
    public boolean isMatch2(String s, String p) {
        int n = s.length();
        int m = p.length();
        boolean[][] dp = new boolean[n + 1][m + 1];
        for (int i = 0; i <= n; i++) {
            for (int j = 0; j <= m ; j++) {
                //空正則和非空正則
                if (j == 0){
                    dp[i][j] = i == 0;
                }else {
                    //非空正則兩種情況
                    if (p.charAt(j - 1) != '*'){
                        if (i > 0 && (s.charAt(i - 1) == p.charAt(j - 1) || p.charAt(j -1) == '.')){
                            dp[i][j] = dp[i - 1][j - 1];
                        }
                    }else {
                        //碰到 * 了，分爲看和不看兩種情況
                        //不看
                        if (j >= 2) {
                            dp[i][j] |= dp[i][j - 2];
                        }
                        //看
                        if (i >= 1 && j >= 2 && (s.charAt(i - 1) == p.charAt(j - 2) || p.charAt(j - 2) == '.')) {
                            dp[i][j] |= dp[i - 1][j];
                        }
                    }
                }
            }
        }
        return dp[n][m];
    }
    
    
    //劍指offer中代碼
    private boolean isMatch3(String s, String p){
        if (s == null || p == null){
            return false;
        }
        char[] strs = s.toCharArray();
        char[] pats = p.toCharArray();
        return matchCore(strs, 0, pats, 0);
    }
    private boolean matchCore(char[] strs, int indexOfStrs, char[] pats, int indexOfPats) {
        if (indexOfStrs == strs.length && indexOfPats ==pats.length){
            return true;
        }
        if (indexOfStrs < strs.length && indexOfPats == pats.length){
            return false;
        }
        if (indexOfPats + 1 < pats.length && pats[indexOfPats + 1] == '*'){
            if ((indexOfStrs < strs.length && pats[indexOfPats] == '.') || (indexOfStrs < strs.length && pats[indexOfPats] == strs[indexOfStrs])){
                return matchCore(strs,indexOfStrs,pats,indexOfPats+2) ||
                        matchCore(strs,indexOfStrs + 1,pats,indexOfPats) ||
                        matchCore(strs,indexOfStrs + 1,pats,indexOfPats + 2);
            }else{
                //向後移動兩個字符，忽略‘*’極前面的字符
                matchCore(strs,indexOfStrs,pats,indexOfPats+2);
            }
        }
        if (indexOfStrs < strs.length && (pats[indexOfPats] == strs[indexOfStrs] || pats[indexOfPats] == '.'))
            return matchCore(strs, indexOfStrs + 1, pats, indexOfPats + 1);
        return false;
    }


    public static void main(String[] args) {
        System.out.println(new Test17().isMatch2("ab", ".*"));
    }
}