/**
 * @param {character[]} s
 * @return {void} Do not return anything, modify s in-place instead.
 */
var reverseString = function(s) {
    let left = 0, right = s.length-1;
    while(left<right){
        const tmp =s[right];
        s[right] = s[left];
        s[left]= tmp;
        left++;
        right--;
    }
};