// Source : https://leetcode.com/problems/decode-string/

// Author : Han Zichi

// Date : 2016-09-05

/**

* @param {string} s

* @return {string}

*/

let decodeString = function(s) {

let nums = []; // 保存数字

let ss = []; // 保存需要 repeat 的字符串

let str = ''; // 当前字符串

let ans = '';

for (let i = 0, len = s.length; i < len; i++) {

let item = s[i];

if (/[0-9]/.test(item)) {

if (i === 0 || /[0-9]/.test(s[i - 1])) {

str += item;

} else {

// s => 2[2[b]]

if (str || s[i - 1] === '[') {

if (nums.length)

ss.push(str);

else

ans += str;

}

str = item;

}

} else if (item === '[') {

nums.push(+str);

str = '';

} else if (item === ']') {

str && ss.push(str);

let count = nums.pop();

let a = ss.pop();

let tmp = a.repeat(count);

if (ss.length) { // 当前有 ss[] 栈

let last = ss.pop();

ss.push(last + tmp);

} else

ans += tmp;

str = '';

} else {

str += item;

}

}

return ans + str;

};