Decode String

• 用两个栈, 一个存储count, 一个存储遇到的string

• 新写的, 遇到了几个问题, 一个是每次遇到'['时忘记讲遇到的str压入栈中, 保证每次都是压入数字, 压入string

• 处理数字时, 尽量利用外层for-loop, 而不是新写一个while

• public class Solution {
      public String decodeString(String s) {
          Stack<Integer> s1 = new Stack<Integer>();
          Stack<String> s2 = new Stack<String>();
          int count = 0;StringBuilder cur = new StringBuilder();
          for(int i=0;i<s.length();){
              if(Character.isDigit(s.charAt(i))){
                  StringBuilder num = new StringBuilder();
                  while(i<s.length()&&Character.isDigit(s.charAt(i))){
                      num.append(s.charAt(i));
                      i++;
                  }
                  count = Integer.valueOf(num.toString());
              }
              if(s.charAt(i)=='['){
                  s1.push(count);
                  s2.push(cur.toString());
                  count = 0;
                  cur.setLength(0);
              }
              else if(s.charAt(i)==']'){
                  StringBuilder tmp = new StringBuilder();
                  int n = s1.pop(); 
                  for(int k=0;k<n;k++){
                      tmp.append(cur.toString());
                  }
  
                  cur = new StringBuilder(s2.pop() + tmp.toString());
              }
              else{
                  cur.append(s.charAt(i));
              }
              i++;
          }
          return cur.toString();
      }
  }
  

更好的版本

public class Solution {
    public String decodeString(String input) {
        Stack<Integer> counts = new Stack<Integer>();
        Stack<String> strs = new Stack<String>();
        String s = ""; int num = 0;
        for(int i=0;i<input.length();i++){
            char c = input.charAt(i);
            if(Character.isDigit(c)){
                    num = num*10 + c-'0';
            }
            else if(c=='['){
                strs.push(s);
                counts.push(num);
                s=""; num=0;
            }
            else if(c==']'){
                int n = counts.pop();
                StringBuilder sb = new StringBuilder();
                for(int j=0;j<n;j++)
                    sb.append(s);
                s = strs.pop() + sb.toString();
            }
            else if(Character.isLetter(c))
                s+=c;
        }
        return s;
    }
}