剑指 Offer 49. 丑数https://leetcode.cn/problems/chou-shu-lcof/

对每个丑数 分别乘2、乘3、乘5 即可得到后续丑数

其中只需要对计算出来的丑数结果进行去重即可

int nthUglyNumber(int n) {

	// base case
	if (n < 1)
	{
		return -1;
	}
	if (n == 1)
	{
		return 1;
	}

	vector<int> res(n);
	res[0] = 1;
	int val2 = 2, val3 = 3, val5 = 5;
	int p2 = 0, p3 = 0, p5 = 0;
	int p = 1;

	while (p != n)
	{
		int minVal = min(val2, min(val3, val5));

		// 去重
		if (minVal != res[p - 1])
		{
			res[p] = minVal;
			++p;
		}
		
		if (minVal == val2)
		{
			++p2;
			val2 = res[p2] * 2;
		}
		else if (minVal == val3)
		{
			++p3;
			val3 = res[p3] * 3;
		}
		else
		{
			++p5;
			val5 = res[p5] * 5;
		}
	}

	return res[n - 1];
}