[394] Decode String

[harrytothemoon]

暴力解法

var decodeString = function(s) {
    let stack = []
    for (let i = 0; i < s.length; i++) {
        if (s[i] !== ']') {
            stack.push(s[i])
            continue
        }
        let str = stack.pop()
        let substr = ''
        while (str !== '[') {
            substr = str + substr
            str = stack.pop()
        }
        let nums = ''
        let num = stack.pop()
        while (!isNaN(Number(num))){
            nums = num + nums
            num = stack.pop()
        }
        stack.push(num)
        stack.push(substr.repeat(Number(nums)))
    }
    return stack.join('')
};

另一種覺得比較直觀的方法

var decodeString = function(s) {
    while(s.indexOf('[') !== -1) { 
        let leftIndex = s.lastIndexOf('[')
        let rightIndex = leftIndex + s.substring(leftIndex).indexOf(']')
        let word = s.substring(leftIndex + 1, rightIndex)
        let count = ""
        leftIndex--
        while(!isNaN(Number(s[leftIndex]))) { 
            count = s[leftIndex] + count
            leftIndex--
        }
        s = s.substring(0, leftIndex + 1) + word.repeat(count) + s.substring(rightIndex + 1)
    }
    return s;
};

[tsungtingdu]

直覺暴力解

var decodeString = function(s) {
  let countStack = [0]
  let strStack = ['']
  let index = 0

  while (index < s.length) {
    let temp = ''

    if (s[index] === ']') {

      // 遇到 ]，往回加入重複字串
      let str = strStack.pop()
      strStack[strStack.length - 1] += str.repeat(countStack.pop())
      index++

    } else if (isNaN(s[index])) {

      // 遇到字母，取完所有字母
      while(isNaN(s[index]) && s[index] !== ']' && index < s.length) {
        temp += s[index]
        index++
      }
      if (strStack.length === countStack.length) {
        strStack[strStack.length - 1] += temp
      } else {
        strStack.push(temp)
      }

    } else if (!isNaN(s[index])) {

      // 遇到數字，取完所有數字
      while(!isNaN(s[index])) {
        temp += s[index]
        index++
      }
      countStack.push(Number(temp))
      if (!isNaN(s[index + 1])) strStack.push('')
      // 跳過 [
      index++
    }
  }
  return strStack[0]
};

[ShihTingJustin]

另類的雙指針

var decodeString = function(s) {
    while (s.indexOf('[') !== -1) {
      let left = s.lastIndexOf('[')
      let right = left + s.substring(left).indexOf(']')
      let str = s.substring(left + 1, right)

      // 拼數字
      let count = ''
      while (s[left-1] <= 9) {
        left--
        count = s[left] + count
      }
      s = s.substring(0, left) + str.repeat(count) + s.substring(right + 1)    // right 是第二次迴圈開始會用到
    }
    return s
};

[henry22]

/**
 * @param {string} s
 * @return {string}
 */
var decodeString = function(s) {
    let num = 0
    let res = ''
    let stack = []

    for(let char of s) {
        if(char === '[') {
            stack.push(res)
            stack.push(num)
            res = ''
            num = 0
        } else if(char === ']') {
            const preNum = stack.pop()
            const preStr = stack.pop()
            res = preStr + res.repeat(preNum)
        } else if(char >= '0' && char <= '9') {
            num = num * 10 + Number(char)
        } else if(char >= 'a' && char <= 'z') {
            res += char
        }
    }

    return res
};