将这些数字按大小排列，用队列即可

class Solution {
public:
    int getUglyNumber(int n) {
        if(n <= 1) return 1;

        vector<int> f(n+1);

        f[1] = 1;

        int l = 1, mid = 1, r = 1;

        for(int i = 2; i <= n; i++){
            int a = f[l] * 2, b = f[mid] * 3, c = f[r] * 5;

            f[i] = min(min(a,b),c);

            if(f[i] == a) l++;
            if(f[i] == b) mid++;
            if(f[i] == c) r++;

        }
        return f[n];
    }
};