原題鏈接https://leetcode.com/problems/k-th-symbol-in-grammar/

題目描述

On the first row, we write a 0. Now in every subsequent row, we look at the previous row and replace each occurrence of 0 with 01, and each occurrence of 1 with 10.

Given row N and index K, return the K-th indexed symbol in row N. (The values of K are 1-indexed.) (1 indexed).

Examples:
Input: N = 1, K = 1
Output: 0

Input: N = 2, K = 1
Output: 0

Input: N = 2, K = 2
Output: 1

Input: N = 4, K = 5
Output: 1

Explanation:
row 1: 0
row 2: 01
row 3: 0110
row 4: 01101001
Note:

N will be an integer in the range [1, 30].
K will be an integer in the range [1, 2^(N-1)].

思路分析

第一行給定為0，之后行依照把0換為01,1換為10的規律

• 利用大一數據結構學的二叉樹，可把規律理解為0的左右子樹分別為0和1，1的子樹分別為1和0
• all in all，
  • 判斷所求的節點是左子節點還是右子節點
  • 判斷他的父節點是0還是1
    //這是一道爆炸友善的題哇ヾ(??▽?)ノ

AC解

class Solution {

    public int kthGrammar(int N, int K) {

        if(K == 1)

        {

            return 0;

        }

        if(N == 1)

        {

            return 0;

        }

        if(K % 2 == 0)

        {

            return kthGrammar(N-1,K/2)==0 ? 1 : 0;

        }

        else

        {

            return kthGrammar(N-1,(K+1)/2)==0 ? 0 : 1;

        }

    }

}

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