LeetCode：214. Shortest palindrome string

Given a string s, You can convert a string to a palindrome string by adding characters in front of it . Find and return the shortest palindrome string that can be converted in this way .

Example 1：

 Input ：s = "aacecaaa"
 Output ："aaacecaaa"

Example 2：

 Input ：s = "abcd"
 Output ："dcbabcd"

Tips ：

• 0 <= s.length <= 5 * 10^4
• s It's only made up of lowercase letters

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### Their thinking 1. First invert the string s, Then traverse the original string , Judge whether the string is palindrome string according to whether the string is equal before and after inversion , So as to find the shortest palindrome string in the original string 2. Finally, directly return the added character plus the original string （ The added character is the string before the shortest palindrome string in the original string ）

Code

/** * @param {string} s * @return {string} */
var shortestPalindrome = function(s) {
    
    const len = s.length
    if (len === 0) return ''
    //  Reverse string s
    let rev = s.split('').reduce((a, b) => b + a, '')
    for (let i = 0; i < len; i++) {
    
        //  Judge whether the string is palindrome string according to whether the string is equal before and after inversion 【rev.slice(i) Namely s.slice(0, len - i) Inverted string of 】
        if (s.slice(0, len - i) === rev.slice(i)) {
    
            //  If it is palindrome string , That is, the shortest palindrome string in the original string 
            return rev.slice(0, i) + s //  Directly return the added character plus the original string 
        }
    }
};