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

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：

[code]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...