Wednesday, February 26, 2020

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);
            }
        }
    };


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