这题目有毒之干不过codewars的OJ系统（二）

Myth丶恋晨 2022-05-26 07:40 145阅读 0赞

## kata ##

**<4kyu>Guess the Digits and Expression**  
Description:  
Give you a multiplication arithmetic expression:

ABC
                *   CBA
                -------             = 39483

Each character represents a diffrent digit(1-9), and you need to find the arithmetic expression and return the result like this:`"123 * 321 = 39483"`

## solutions ##

**这是我的解决方案：**

function guessExpression(exp){ 
      let expression = ''
      const reg = /\s*(\w+)\n\*\s*(\w+)\n.*\n[\D]*(\d+)/g
      const unitArr = reg.exec(exp).slice(1)
      const [aDigit, bDigit] = unitArr
      const aDigitLast = aDigit[aDigit.length - 1]
      const bDigitLast = bDigit[bDigit.length - 1]
      const digitList = [...new Set(aDigit)]
      const numResult = parseInt(unitArr[2])
      const isOdd = numResult % 2 === 1
      function vEach(strs, stat = {}) { 
        const firstStr = strs[0]
        for (let i of [1, 2, 3, 4, 5, 6, 7, 8, 9]) {
          if (expression) return
          stat[firstStr] = i
          if (strs.length > 1) {
            vEach(strs.slice(1), stat)
          } else {
            const realADigit = [].map.call(aDigit, v => stat[v]).join('')
            const realBDigit = [].map.call(bDigit, v => stat[v]).join('')
            if (realADigit[0] && realBDigit[0] && (~~realADigit * ~~realBDigit === numResult)) {
    
              expression = `${realADigit} * ${realBDigit} = ${numResult}`
              if (realADigit.split('').reverse().join('') === realBDigit) {
                const min = Math.min(~~realADigit, ~~realBDigit)
                const max = Math.max(~~realADigit, ~~realBDigit)
                expression = `${min} * ${max} = ${numResult}`
              }
            }
          }
        }
      }
      vEach(digitList.join(''))
      return expression
    }

提交时报错：execution time out 12000ms  
后来想到如果乘积为奇数，则两乘数也为奇数，如果乘积为偶数，则两乘数必有一个为偶数  
所以有如下的优化：

......
    const firstStr = strs[0]
        let mapArr = []
        if (isOdd) {
          if (firstStr === aDigitLast || firstStr === bDigitLast) {
            mapArr = [1, 3, 5, 7, 9]
          } else {
            mapArr = [1, 2, 3, 4, 5, 6, 7, 8, 9]
          }
        } else {
          if (firstStr === aDigitLast || firstStr === bDigitLast) {
            if (aDigitLast % 2 === 1 && firstStr !== aDigitLast) {
              mapArr = [2, 4, 6, 8]
            } else if (bDigitLast % 2 === 1 && firstStr !== bDigitLast) {
              mapArr = [2, 4, 6, 8]
            } else {
              mapArr = [1, 2, 3, 4, 5, 6, 7, 8, 9]
            }
          } else {
            mapArr = [1, 2, 3, 4, 5, 6, 7, 8, 9]
          }
        }
        for (let i of mapArr) {
          if (expression) return
        ......

然而并没有什么卵用，执行时间几乎和之前的算法一样。  
如此，在网络上搜索相关答案，找到**某大佬的解决方案：**

使用`console.time`测试了下，大佬的解法用时几乎是我解法的一半。  
令人沮丧的是：codewars的OJ用大佬的解法也没有通过测试，我不知道要如何optimize my solution.

## 相关链接 ##

*  [Train: Guess the Digits and Expression | Codewars][Train_ Guess the Digits and Expression _ Codewars]
 *  [大佬的解决方案][Link 1]

[Train_ Guess the Digits and Expression _ Codewars]: https://www.codewars.com/kata/57f9bbe759eb61a049000160/train/javascript
[Link 1]: https://github.com/gkucmierz/codewars/blob/master/guess-the-digits-and-expression/index.js