1. /**
    2.  * @param {string} s
    3.  * @return {string}
    4.  */
    5. // 递归法
    6. var decodeString = function(s) {
    7.   const o = {
    8.     '[': 1,
    9.     ']': -1,
    10.   }
    11.   const num = ['1', '2', '3', '4', '5', '6', '7', '8', '9', '0']
    12.   function copy(str, ind) {
    13.     let newStr = ''
    14.     let i = ind;
    15.     while (i < str.length) {
    16.       if (num.includes(str[i])) {
    17.         const index = str.indexOf('[')
    18.         const count = +(str.substr(i, index - i));
    19.         let tempS = ''
    20.         let t = 0;
    21.         for (let j = index; j < str.length; j++) {
    22.           if (o[str[j]] !== undefined) {
    23.             t += o[str[j]]
    24.             if (t === 0) {
    25.               tempS = str.substr(index + 1, j - index - 1);
    26.               i = j + 1;
    27.               for (let k = 0; k < count; k++) {
    28.                 newStr += tempS;
    29.               }
    30.               newStr += str.substr(j + 1);
    31.               if (newStr.indexOf('[') > -1) {
    32.                 newStr = copy(newStr, j + 1)
    33.               }
    34.               return newStr
    35.             }
    36.           }
    37.         }
    38.       } else {
    39.         newStr += str[i]
    40.         i++;
    41.       }
    42.     }
    43.     return newStr
    44.   }
    45.   console.log(copy(s, 0));
    46.   return copy(s, 0)
    47. };
    49. // 栈堆法
    50. var decodeString2 = (s) => {
    51.   let stack = []
    52.   for (const char of s) {
    53.     if (char !== ']') { // ] 前的字符都入栈
    55.       stack.push(char)
    56.       // console.log(stack);
    57.       continue
    58.     }
    59.     let cur = stack.pop() // 弹出一个来检测
    60.     let str = '' // 组装字符串
    61.     // 接下来肯定是遇到字母，直到遇到 [
    62.     while (cur !== '[') {
    63.       str = cur + str // cur字符加在左边
    64.       cur = stack.pop() // 再拉出一个
    65.     }
    66.     // 此时cur为 [，接下来要遇到数字
    67.     let num = ''
    68.     cur = stack.pop() // 用下一个将 [ 覆盖
    69.     while (!isNaN(cur)) {
    70.       num = cur + num // 数字字符加在左边
    71.       cur = stack.pop() // 再拉出一个
    72.     }
    73.     // 现在要么是字母，要么是 [
    74.     console.log(cur);
    75.     stack.push(cur)
    76.     for (let j = 0; j < num; j++) {
    77.       stack.push(str)
    78.     }
    79.   }
    80.   console.log(stack.join(''), `stack.join('')`);
    81.   return stack.join('')
    82. }
    84. decodeString2('x2[3[a]r4[ff]]hhh')