680. Valid Palindrome II

package LeetCode_680

/**
 * 680. Valid Palindrome II
 * https://leetcode.com/problems/delete-operation-for-two-strings/description/
 *
 * Given two words word1 and word2, find the minimum number of steps required to make word1 and word2 the same, where in each step you can delete one character in either string.

Input: "sea", "eat"
Output: 2
Explanation: You need one step to make "sea" to "ea" and another step to make "eat" to "ea".

Note:
The length of given words won't exceed 500.
Characters in given words can only be lower-case letters.
 * */
class Solution {
    //Time complexity:O(n)
    fun validPalindrome(s: String): Boolean {
        //var l = -1
        val n = s.length
        var l = 0
        var r = n-1
        while (l < r && s[l] == s[r]) {
            l++
            r--
        }
        //if left,right char is not equal, either delete one char in left or delete one char in right and check again
        return isPalindrome(s, l + 1, r) || isPalindrome(s, l, r - 1)
    }

    private fun isPalindrome(str: String, l_: Int, r_: Int): Boolean {
        var l = l_
        var r = r_
        while (l < r) {
            if (str[l] != str[r]) {
                return false
            }
            l++
            r--
        }
        return true
    }
}