Strings
Palindrome
A palindrome is a word, number, phrase, or other sequence of characters which reads the same backward as forward.
Author@wkw
Overview
A palindrome reads the same forward and backward. amanaplanacanalpanama and 10101 are the examples of palindrome.
There are multiple ways to check if a string is a palindrome or not.
Iteration
As we know it reads the same forward and backward, which means is same as , is same as and so on. Therefore, we can iterate times to check if the left side is same as the right side.
bool isPalindrome(const string& s) {
for (int i = 0; i < s.size() / 2; i++) {
if (s[i] != s[s.size() - i - 1]) {
return false;
}
}
return true;
}Built-in Functions
We can directly use built-in function to reverse a string and check if it is same as the target one.
bool isPalindrome(const string& s) {
string t = s;
reverse(t.begin(), t.end());
return s == t;
}bool isPalindrome(const string& s) {
return s == string(s.rbegin(), s.rend());
}bool isPalindrome(const string &s) {
return equal(s.begin(), s.begin() + s.size() / 2, s.rbegin());
}Palindrome with Range
For a given range, we can follow the same idea to use two pointers to check if a sub-string is a palindrome .
bool palindromeWithRange(string s, int i, int j) {
while (i < j) {
if (s[i] != s[j]) return false;
i++, j--;
}
return true;
}