原文:36. 有效的数独(力扣 面试题) - 每天一个JavaScript小知识@Js中文网 · 码农进阶题库

原文地址:https://www.javascriptc.com/interview-tips/zh_cn/leetcode/leetcode-javascript-solution-036/

题目:

难度:Middle

相关话题:哈希表

判断一个9x9 的数独是否有效。只需要根据以下规则 ,验证已经填入的数字是否有效即可。

  1. 数字 1-9 在每一行只能出现一次。

  2. 数字 1-9 在每一列只能出现一次。

  3. 数字 1-9 在每一个以粗实线分隔的 3x3 宫内只能出现一次。

上图是一个部分填充的有效的数独。

数独部分空格内已填入了数字,空白格用 '.' 表示。

示例1:

输入:
[
  ["5","3",".",".","7",".",".",".","."],
  ["6",".",".","1","9","5",".",".","."],
  [".","9","8",".",".",".",".","6","."],
  ["8",".",".",".","6",".",".",".","3"],
  ["4",".",".","8",".","3",".",".","1"],
  ["7",".",".",".","2",".",".",".","6"],
  [".","6",".",".",".",".","2","8","."],
  [".",".",".","4","1","9",".",".","5"],
  [".",".",".",".","8",".",".","7","9"]
]
输出: true

示例2:

输入:
[
 ["8","3",".",".","7",".",".",".","."],
 ["6",".",".","1","9","5",".",".","."],
 [".","9","8",".",".",".",".","6","."],
 ["8",".",".",".","6",".",".",".","3"],
 ["4",".",".","8",".","3",".",".","1"],
 ["7",".",".",".","2",".",".",".","6"],
 [".","6",".",".",".",".","2","8","."],
 [".",".",".","4","1","9",".",".","5"],
 [".",".",".",".","8",".",".","7","9"]
]
输出: false
解释: 除了第一行的第一个数字从5 改为 8以外,空格内其他数字均与 示例1 相同。
     但由于位于左上角的 3x3 宫内有两个 8 存在, 因此这个数独是无效的。

说明:

  • 一个有效的数独(部分已被填充)不一定是可解的。

  • 只需要根据以上规则,验证已经填入的数字是否有效即可。

  • 给定数独序列只包含数字 1-9 和字符 '.'

  • 给定数独永远是 9x9 形式的。


思路:

因为存在9行,9列,93*3的格子,因此可以遍历[0,9],分别检查对应索引的行,列和块。

具体检查步骤就是创建hash,如果内部存在相同的数字,则返回false

行列检查都很简单,块需要将id转化为行开始的索引,行结束的索引,列开始的索引,列结束的索引。

[行开始,行结束][Math.floor(id/3)*3,Math.floor(id/3)*3+2]

[列开始,列结束][id%3*3,id%3*3+2]

/**
 * @来源: Javascript中文网 - 前端进阶资源教程 https://www.javascriptc.com/
 * @介绍:JS中文网是中国领先的新一代开发者社区和专业的技术媒体,一个帮助开发者成长的社区,目前已经覆盖和服务了超过 300 万开发者,你每天都可以在这里找到技术世界的头条内容
 * @param {character[][]} board
 * @return {boolean}
 */
var isValidSudoku = function(board) {
  function rowIsValid(id){
    let hash={}
    for(let i=0;i<board[id].length;i++){
      let cur=board[id][i]
      if(hash[cur])return false
      if(cur!=='.')hash[cur]=true
    }
    return true
  }
  function colIsValid(id){
    let hash={}
    for(let i=0;i<board.length;i++){
      let cur=board[i][id]
      if(hash[cur])return false
      if(cur!=='.')hash[cur]=true
    }
    return true
  }
  function boxIsValid(id){
    let f=Math.floor(id/3),
        m=id % 3
    let rs=f*3,re=f*3+2,
        cs=m*3,ce=m*3+2
    let hash={}
    for(let i=rs;i<=re;i++){
      for(let j=cs;j<=ce;j++){
        let cur=board[i][j]
        if(hash[cur])return false
        if(cur!=='.')hash[cur]=true
      }
    }
    return true
  }

  for(let i=0;i<9;i++){
    if(!rowIsValid(i) || !colIsValid(i) || !boxIsValid(i))return false
  }
  return true
};

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