【剑指offer33 丑数】

class Solution {
public:
    /*
    bool check(int x){
        while(x%2==0)x/=2;
        while(x%3==0)x/=3;
        while(x%5==0)x/=5;
        if(x==1)return true;
        else return false;
    }*/
    
    
    int GetUglyNumber_Solution(int index) {
        /*
        //会超时 
        if(index==1)return 1;
        int cnt = 0 ;
        int x = 1 ;
        while(1){
            if(check(x)){
                cnt++;
                if(cnt == index)break;
            }
            ++x ;
        }
        return x;*/
        
        if(index<7)return index; //7之前都是丑数
        vector<int> ans(index);
        int t2=0, t3=0 , t5=0;//分别做乘的位置标记
        ans[0]=1 ;
        for(int i=1 ; i<index ; ++i){
            ans[i] = min(ans[t2]*2 , min(ans[t3]*3 , ans[t5]*5));
            if(ans[i] == ans[t2]*2)t2++; //谁做了乘法 就下标往后移动一格
            if(ans[i] == ans[t3]*3)t3++;
            if(ans[i] == ans[t5]*5)t5++;
        }
        return ans[index-1];
    }
};