題目:
把隻包含質因子2、3和5的數稱作醜數(Ugly Number)。例如6、8都是醜數,但14不是,因為它包含質因子7。 習慣上我們把1當做是第一個醜數。求按從小到大的順序的第N個醜數。
class Solution {
public:
int GetUglyNumber_Solution(int index)
{
if (index < 7)
return index;
vector<int> res(index);
res[0] = 1;
int t2 = 0, t3 = 0, t5 = 0, i;
for (i = 1; i < index; ++i)
{
res[i] = min(res[t2] * 2, min(res[t3] * 3, res[t5] * 5));
if (res[i] == res[t2] * 2)
t2++;
if (res[i] == res[t3] * 3)
t3++;
if (res[i] == res[t5] * 5)
t5++;
}
return res[index - 1];
}
};