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// [0, n)の値をn個ランダムで生成した配列を返す
function makeRandomNumberArr(n) {
    let arr = [];
    let i = 0;
    let num;
    while(i < n) {
        num = Math.floor(Math.random() * n);
        if(~arr.indexOf(num)) continue;
        arr.push(num);
        i++;
    }
    return arr;
}