delete repeat（去重）

function set (arr) {
    let len = arr.length;

    for (let i = 0; i < len-1; i++) {
        for (let j = i+1; j < len; j++) {
            if (arr[i] === arr[j]) {
                arr.splice(j, 1);
                len = arr.length;
                j--;
            }
        }
    }
}