输入: [2,0,2,1,1,0]
输出: [0,0,1,1,2,2]

let sortColors = function(nums) {
    let colors = [0, 0, 0]

    for (let i = 0; i < nums.length; i++) {
        colors[nums[i]] ++
    }

    nums.length = 0
    for (let i = 0; i < colors.length; i++) {
        for(let j = 0; j < colors[i]; j++) {
            nums.push(i)
        }
    }
};