查找字符串中最长的回文

// 暴力破解 O(n^3)
var longestPalindrome = function(s) {
    var result = []
    const sArr = s.split('')
    for(let i=0;i<sArr.length;i++){
        for(let j=0;j<sArr.length;j++){
            let tempArr = sArr.slice(i,j)
            let flag = true
            for(let k=0;k<tempArr.length/2;k++){
                if(tempArr[k] !== tempArr[tempArr.length-1-k]){
                    flag = false
                }
            }
            if(flag && tempArr.length){
                if(result.length < tempArr.length){
                    result = tempArr
                }
            }
        }
    }
    return result
};

// 中间向两边延伸O(n^2)
var longestPalindrome = function (s) {
    var result = ""
    for (let i = 0; i < s.length; i++) {
        let temp = ""
        let temp1 = isPalindrome(s, i-1, i+1)
        let temp2 = isPalindrome(s, i, i+1)
        temp = temp1.length > temp2.length ? temp1 : temp2
        if (result.length <= temp.length) {
            result = temp
        }
    }
   if (result == "") {
        return s.charAt(0)
    }
    return result

};
var isPalindrome = function (s, low, high) {
    let result = ""
    while (low >= 0 && high < s.length) {
        if (s.charAt(low) == s.charAt(high)) {
            const temp = s.substring(low, high + 1)
            if (result.length <= temp.length) {
                result = temp
            }
            low--
            high++
        }else{
            break
        }
    }
    return result
}

还可以进行优化对某些判断获得字符传进行缓存