剑指Offer 49 丑数

一道经典ACM题目。

将丑数打表，然后求解即可。

打表思路：

丑数*2 = 新的丑数a

丑数*3 = 新的丑数b

丑数*5 = 新的丑数c

为了表格里面的丑数从小到大排序，需要从三个丑数中取最小的丑数，然后插入数组，然后将2或3或5的位置计数+1。

class Solution {
    static final int SIZE = 1691;
    static int record[] = new int[SIZE];

    public static void init() {
        if(record[0] == 1)
            return;
        record[0] = 1;
        int i=1;
        int indexTwo = 0;
        int indexThree = 0;
        int indexFive = 0;
        while(i<SIZE) {
            int resTwo = record[indexTwo] * 2;
            int resThree = record[indexThree] * 3;
            int resFive = record[indexFive] * 5;
            int minRes = Math.min(Math.min(resTwo, resThree), resFive);
            if(minRes == resTwo)
                indexTwo ++;
            if(minRes == resThree)
                indexThree++;
            if(minRes == resFive)
                indexFive++;
            record[i] = minRes;
            i++;
        }
    }


    public int nthUglyNumber(int n) {
        init();
        return record[n-1];
    }
}