394. Decode String

 

用curString去记录前面的String的结果

 

class Solution {
    public String decodeString(String s) {
        if(s.length() == 0) return "";
        char[] arr = s.toCharArray();
        Stack<String> stack = new Stack<>();
        int i = 0;
        String curString = "";
        while(i < s.length()){
            if(Character.isDigit(arr[i])){
                String num = "";
                while(Character.isDigit(arr[i])){
                    num += arr[i];
                    i++;
                }
                stack.push(num);
            }
            if(arr[i] == '['){
                stack.push(curString);
                curString = "";
                i++;
                continue;
            }
            if(arr[i] == ']'){
                String prev = stack.pop();
                String num = stack.pop();
                int j = Integer.parseInt(num);
                String temp = curString;
                for(int k = 0; k < j-1; k++){
                    curString += temp; 
                }
                curString = prev + curString;
                i++;
            }else{
                curString += arr[i]; 
                i++;
            }
            
        }
        return curString;    
    }
}