Decode String

Decode String

题目链接：https://leetcode.com/problems...

stack的题，感觉还是分析下stack什么时候pop，什么时候push，思路会比较快。loop里面不加while循环的写法。

public class Solution {
    public String decodeString(String s) {
        /* stack to solve: store string & store number
         * 2 variables: str, number
         * 1. push: meet '['
         *          number to numberStack, str to stringStack
         *          reset number & str
         * 2. pop: meet ']'
         *         pop number & str, append current str
         * 3. meet number: update number
         * 4. meet other characters: update str
         * result: s
         */
         Stack<String> stringStack = new Stack();
         Stack<Integer> numberStack = new Stack();
         String str = "";
         int number = 0;
         for(int i = 0; i < s.length(); i++) {
             char c = s.charAt(i);
             if(c == '[') {
                 // push
                 stringStack.push(str);
                 numberStack.push(number);
                 str = "";
                 number = 0;
             }
             else if(c == ']') {
                 String temp = str;
                 str = stringStack.pop();
                 for(int j = numberStack.pop(); j > 0; j--) {
                     str += temp;
                 }
             }
             else if(c >= '0' && c <= '9') number = number * 10 + (c-'0');
             else str += c;
         }
         
         return str;
    }
}