Interview Classic 150 P125: Valid Palindrome

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Timeline

Timeline

2025-10-17

init

string

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Problem:

P125 Valid Palindrome

https://leetcode.cn/problems/valid-palindrome/description/?envType=study-plan-v2&envId=top-interview-150

Using two pointers would definitely be faster, but here I directly used the standard library’s reverse.

#include <algorithm>
#include <cstring>
#include <string>
using std::string;

class Solution {
public:
  bool isPalindrome(string s) {
    int i;
    int n = s.size();
    string original;

    for (i = 0; i < n; i++) {
      if (s[i] >= 'A' && s[i] <= 'Z')
        s[i] = s[i] - ('A' - 'a');
      
      if (!(s[i] >= 'a' && s[i] <= 'z') && !(s[i] >= '0' && s[i] <= '9'))
        s[i] = '*';
    }

    s.erase(std::remove(s.begin(), s.end(), '*'), s.end());

    original = s;
    std::reverse(s.begin(), s.end());

    if (std::strcmp(s.c_str(), original.c_str()) == 0)
      return true;
    else
      return false;
  
  }
};