717. 1-bit and 2-bit Characters (easy)

Q:

We have two special characters. The first character can be represented by one bit 0. The second character can be represented by two bits (10 or 11).

Now given a string represented by several bits. Return whether the last character must be a one-bit character or not. The given string will always end with a zero.

Example 1:

Input: 
bits = [1, 0, 0]
Output: True
Explanation: 
The only way to decode it is two-bit character and one-bit character. So the last character is one-bit character.

Example 2:

Input: 
bits = [1, 1, 1, 0]
Output: False
Explanation: 
The only way to decode it is two-bit character and two-bit character. So the last character is NOT one-bit character.

Note:

1 <= len(bits) <= 1000.

bits[i] is always 0 or 1.

A:

本以为 需要DP， 结果不用。  

class Solution {
public:
    bool isOneBitCharacter(vector<int>& bits) {
        return helper(bits, 0);            
    }
private:
    bool helper(vector<int> &bits, int i)
    {
        int n = bits.size();
        if(i>=n)
            return false;
        if(i==n-1)
            return bits[i]==0;
        // we have at least two bits
        if(bits[i]==0){
            return helper(bits,i+1);
        }else{
            return helper(bits, i+2);
        }
    }
};