题解 | #字符串解码#

import java.util.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param s string字符串 
     * @return string字符串
     */
    
    /**********************************************************************************/
    // 用力通过率: 80%
    /*
    public String decodeString (String s) {
        // write code here
        Stack<Character> stack = new Stack<>();
        char[] chrs = s.toCharArray();
        StringBuffer sb = new StringBuffer("");
        for (char chr : chrs) {
            if (chr == '[') {
                stack.push(chr);
            }
            else if (chr == ']') {
                stack.pop();
                StringBuffer tmpSB = new StringBuffer("");
                while (!stack.isEmpty() && stack.peek() != '[') {
                    tmpSB.append(stack.pop());
                }
                tmpSB.reverse();
                int num = Integer.valueOf(new String(tmpSB)); // 字符串要复制多少次
                StringBuffer copySB = new StringBuffer(new String(sb));
                for (int i = 1; i < num; i++) { // 复制(复制的次数要少一次，毕竟自己也算一次了嘛)
                    sb.append(copySB);
                }
            }
            else if (chr >= '0' && chr <= '9') { // 如果是数字，直接入栈
                stack.push(chr);
            }
            else { // 英文字母
                sb.append(chr);
            }
        }
        return new String(sb);
    }
    */
    
    /**********************************************************************************/
    // 用力通过率: 100%
    public String decodeString (String s) {
        
        if (1 == s.length()) {
            return s;
        }
        
        Stack<Integer> numStack = new Stack<>();
        Stack<String> strStack = new Stack<>();
        StringBuffer res = new StringBuffer("");
        char[] chrs = s.toCharArray();
        for (int i = 0; i < chrs.length; i++) {
            if (chrs[i] >= '0' && chrs[i] <= '9') {
                int num = chrs[i] - '0';
                while (i + 1 < chrs.length && chrs[i + 1] >= '0' && chrs[i + 1] <= '9') {
                    num = num * 10 + (chrs[i + 1] - '0');
                    i++;
                }
                numStack.push(num);
            }
            else if (chrs[i] == '[') {
                strStack.push(new String(res));
                res = new StringBuffer("");
            }
            else if (chrs[i] == ']') {
                StringBuffer tmp = new StringBuffer(strStack.pop());
                int num = numStack.pop();
                for (int j = 0; j < num; j++) {
                    tmp.append(res);
                }
                res = tmp;
            }
            else {
                res.append(chrs[i]);
            }
        }
        return new String(res);
    }
}