/**
 * @param {character[]} s
 * @return {void} Do not return anything, modify s in-place instead.
 */
var reverseString = function(s) {
    let len = s.length, half = len>>1;
    for (let i=0;i<half;i++) {
        if (i !== len-1-i) {
            [s[i], s[len-1-i]] = [s[len-1-i], s[i]];
        }
    }
    return s;
};

console.info(reverseString(["H","a","n","N","a","h", "9"]));