Valid Palindrome

问题：

Given a string, determine if it is a palindrome, considering only alphanumeric characters and ignoring cases.

思路：

　　简单的数学推导

我的代码:

public class Solution {
    public boolean isPalindrome(String s) {
        if(s == null || s.length() == 0)  return true;
        int left = 0;
        int right = s.length() - 1;
        while(left < right)
        {
            while(!isAlpha(s.charAt(left)) && left < right) left++;
            while(!isAlpha(s.charAt(right)) && left < right) right--;
            if(!isEqual(s.charAt(left), s.charAt(right))) return false;
            left ++;
            right --;
        }
        return true;
    }
    public boolean isAlpha(char c)
    {
        return ((c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9'));
    }
    public boolean isEqual(char left, char right)
    {
       return (left == right || Math.abs(left-right) == 32);
    }
}

View Code

他人代码：

public class Solution {
    public boolean isPalindrome(String s) {
        if (s == null || s.length() == 0) {
            return true;
        }

        int front = 0;
        int end = s.length() - 1;
        while (front < end) {
            while (front < s.length() && !isvalid(s.charAt(front))){ // nead to check range of a/b
                front++;
            }

            if (front == s.length()) { // for emtpy string “.,,,”     
                return true; 
            }           

            while (end >= 0 && ! isvalid(s.charAt(end))) { // same here, need to check border of a,b
                end--;
            }

            if (Character.toLowerCase(s.charAt(front)) != Character.toLowerCase(s.charAt(end))) {
                break;
            } else {
                front++;
                end--;
            }
        }

        return end <= front; 
    }

    private boolean isvalid (char c) {
        return Character.isLetter(c) || Character.isDigit(c);
    }
}

View Code

学习之处：

Character.isLetter(c) Character.isDigit(c) Character.toLowerCase(c) Character还有这几个API不错
写代码的时候，尽量的简洁和功能划分，比如我的代码里面的isAlpha和isEqual都可以用一行代码解决，这样就不要用多行，注意功能划分。