25. Valid Palindrome

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Valid Palindrome

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

For example, "A man, a plan, a canal: Panama" is a palindrome. "race a car" is not a palindrome.

Note: Have you consider that the string might be empty? This is a good question to ask during an interview.

For the purpose of this problem, we define empty string as valid palindrome.

思想：簡單的從兩端來逐個讀字元，判斷是否相等。(36ms)

inline char getLowerChar(string &s, int id) {    if((s[id] >= ‘a‘ && s[id] <= ‘z‘) || (s[id] >= ‘0‘ && s[id] <= ‘9‘)) return s[id];    else if(s[id] >= ‘A‘ && s[id] <= ‘Z‘)  return s[id] + 32;    else return 0;}inline char getFirstChar(string &s, int& l) {    while(l < s.size()) {        char ch = getLowerChar(s, l);        if(ch) return ch;        ++l;    }    return 0;}inline char getLastChar(string &s, int& h) {    while(h >= 0) {        char ch = getLowerChar(s, h);        if(ch) return ch;        --h;    }    return 0;}class Solution {public:    bool isPalindrome(string s) {        int l = 0, h = s.size()-1;        while(l <= h) {            if(getFirstChar(s, l) != getLastChar(s, h))                 return false;                ++l, --h;        }        return true;            }};

 

25. Valid Palindrome