#1616 - Split Two Strings to Make Palindrome

Problem Description

You are given two strings a and b of the same length. Choose an index and split both strings at the same index, splitting a into two strings: aprefix and asuffix where a = aprefix + asuffix, and splitting b into two strings: bprefix and bsuffix where b = bprefix + bsuffix. Check if aprefix + bsuffix or bprefix + asuffix forms a palindrome.

When you split a string s into sprefix and ssuffix, either ssuffix or sprefix is allowed to be empty. For example, if s = "abc", then "" + "abc", "a" + "bc", "ab" + "c" , and "abc" + "" are valid splits.

Return true if it is possible to form a palindrome string, otherwise return false.

Notice that x + y denotes the concatenation of strings x and y.

Solution

/**
 * @param {string} a
 * @param {string} b
 * @return {boolean}
 */
var checkPalindromeFormation = function(a, b) {
  return check(a, b) || check(b, a);

  function isPalindrome(str, left, right) {
    while (left < right) {
      if (str[left++] !== str[right--]) return false;
    }
    return true;
  }

  function check(str1, str2) {
    let left = 0;
    let right = str1.length - 1;

    while (left < right && str1[left] === str2[right]) {
      left++;
      right--;
    }

    return isPalindrome(str1, left, right) || isPalindrome(str2, left, right);
  }
};