leetcode DecodeString
z
 2019-04-09 10:36:27   
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import java.util.Stack;

public class DecodeString {
  /**
   * Given an encoded string, return it's decoded string.
   *
   * The encoding rule is: k[encoded_string], where the encoded_string inside the square brackets is being repeated exactly k times.
   * Note that k is guaranteed to be a positive integer.
   *
   * You may assume that the input string is always valid; No extra white spaces, square brackets are well-formed, etc.
   *
   * Furthermore, you may assume that the original data does not contain any digits and that digits are only for those repeat numbers, k.
   * For example, there won't be input like 3a or 2[4].
   *
   * Examples:
   *
   * s = "3[a]2[bc]", return "aaabcbc".
   * s = "3[a2[c]]", return "accaccacc".
   * s = "2[abc]3[cd]ef", return "abcabccdcdcdef".
   */
  public String decodeString(String s) {
    Stack<String> stringStack = new Stack<>();
    Stack<Integer> numStack = new Stack<>();
    String temp = "";

    for (int i=0; i<s.length(); i++){
      if (Character.isDigit(s.charAt(i))){
        int count = s.charAt(i) - '0';
        while(Character.isDigit(s.charAt(i+1))){
          count = count*10+ s.charAt(i) - '0';
          i = i+1;
        }
        numStack.push(count);
      }

      else if (s.charAt(i) == '['){
        stringStack.push(temp);
        temp = "";
      }

      else if (s.charAt(i) == ']'){
        StringBuilder sb = new StringBuilder(stringStack.pop());
        int repeatTime = numStack.pop();
        for (int j=0; j<repeatTime; j++){
          sb.append(temp);
        }
        temp = sb.toString();
      }
      else{
        temp = temp + s.charAt(i);
      }
    }
    return temp;
  }
}