三指针方法

import java.util.*;
// 时间O(N)空间O(N)
public class Solution {
    public int GetUglyNumber_Solution(int index) {
        // 1 2 3 4 5 6
        if(index <= 6) return index;
        
        int i2 = 0,i3 = 0,i5 = 0;
        int[] res = new int[index];
        res[0] = 1;
        
        for(int i=1;i<index;i++){
            res[i] = Math.min(res[i2]*2,Math.min(res[i3]*3,res[i5]*5));
            
            if(res[i] == res[i2]*2) i2++;
            
            if(res[i] == res[i3]*3) i3++;
            
            if(res[i] == res[i5]*5) i5++;
        }
        return res[index-1];
    }
}