650. 2 Keys Keyboard

Initially on a notepad only one character 'A' is present. You can perform two operations on this notepad for each step:

1. Copy All: You can copy all the characters present on the notepad (partial copy is not allowed).
2. Paste: You can paste the characters which are copied last time.

只能使用1.复制全部 2. 粘贴 两种操作，复制得一定长度字符串。求最小步数。

Given a number n. You have to get exactly n 'A' on the notepad by performing the minimum number of steps permitted. Output the minimum number of steps to get n 'A'.
Example 1:

Input: 3
Output: 3
Explanation:
Initially, we have one character 'A'.
In step 1, we use Copy All operation.
In step 2, we use Paste operation to get 'AA'.
In step 3, we use Paste operation to get 'AAA'.

Note:
The n will be in the range [1, 1000].

---

这题不是DP， 用数学解法就行。

class Solution {
    public int minSteps(int n) {
        int res = 0;
        while(n>1){
            int d = findDivider(n);
            res += d;
            n /= d;
        }
        return res;
    }
    public int findDivider(int n){
        for(int d=2;d<=Math.sqrt(n);d++){
            if(n%d==0) return d;
        }
        return n;
    }
}