K-th Symbol in Grammar——LeetCode进阶路
原题链接https://leetcode.com/problems/k-th-symbol-in-grammar/
题目描述
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
第一行给定为0,之后行依照把0换为01,1换为10的规律
- 利用大一数据结构学的二叉树,可把规律理解为0的左右子树分别为0和1,1的子树分别为1和0
- all in all,
- 判断所求的节点是左子节点还是右子节点
- 判断他的父节点是0还是1
//这是一道爆炸友善的题哇ヾ(✿゚▽゚)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;
}
}
}