LeetCode-探索-初级-字符串-验证回文字符串-java

给定一个字符串，验证它是否是回文串，只考虑字母和数字字符，可以忽略字母的大小写。

说明：本题中，我们将空字符串定义为有效的回文串。

示例 1:

输入: "A man, a plan, a canal: Panama"
输出: true

示例 2:

输入: "race a car"
输出: false

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方法比较简单，就是从前到后一个一个比就行，直接贴代码了：

public boolean isPalindrome(String s) {
        if (s.length() <= 1)
            return true;
        int rear = s.length() -1, front = 0;
        char[] target = s.toCharArray();
        for ( ; ; ) {
            while (front < s.length() && !isValid(target[front])) {
                front ++;
            }    //find the next valid char in "target"
            while (rear >= 0 && !isValid(target[rear])) {
                rear --;
            }    //find the next valid char in "target"
            if (front < rear && front < s.length() && rear >= 0) {
                if (isEqualIgnoreCase(target[rear], target[front])) {
                    rear --;
                    front ++;
                    continue;
                } else {
                    return false;
                }
            } else {
                return true;
            }
        }
    }
    //--------------------------------------------------------------------
    public boolean isLetter(char c) {
        return isLowercase(c) || isUpperCase(c);
    }

    public boolean isUpperCase(char c) {
        return c >= 'A' && c <= 'Z';
    }

    public boolean isLowercase(char c) {
        return c >= 'a' && c <= 'z';
    }

    public boolean isNumber(char c) {
        return c >= '0' && c <= '9';
    }

    public boolean isValid(char c) {
        return isNumber(c) || isLetter(c);
    }

    public boolean isEqualIgnoreCase(char c1, char c2) {
        if (isLowercase(c1))
            c1 = (char) (c1 - 'a' + 'A');
        if (isLowercase(c2))
            c2 = (char) (c2 - 'a' + 'A');
        //convert lowercase to uppercase
        return c1 == c2;
    }
    //---------------------------------------------------------------------------------
    public boolean isPalindrome0(String s) {
        if (s.length() <= 1)
            return true;
        char[] source = s.toCharArray();
        int index = 0;
        for (int i = 0 ; i < source.length ; i ++)
            if (isValid(source[i]))
                source[index ++] = source[i];
        //index is the position to be added.
        if (index == 0)
            return true;
        for (int i = 0 ; i < index ; i ++)
            if (!isEqualIgnoreCase(source[i], source[index - 1 - i]))
                return false;
        return true;
    }

写了两种方法，第二种，就当我没试过...