271. Encode and Decode Strings

    /*
     * 271. Encode and Decode Strings
     * 2016-6-25 by Mingyang
     * 这道题很酷的地方就是选择一种存储方式可以有效地存储string，我一开始就想到了存长度加string的方法
     * 这个题用了一个indexof的API，
     * public int indexOf(String str,int fromIndex)
     * Returns the index within this string of the first occurrence of the specified substring,
     * starting at the specified index.The returned index is the smallest value k for which:
     * k >= fromIndex && this.startsWith(str, k)
     * 就是说从fromIndex以后的第一次出现str的index
     */
      // Encodes a list of strings to a single string.
    public String encode(List<String> strs) {
        StringBuilder sb = new StringBuilder();
        for(String s : strs) {
            //这里加的/其实加任何符号都可以
            sb.append(s.length()).append('/').append(s);
        }
        return sb.toString();
    }
    // Decodes a single string to a list of strings.
    public List<String> decode(String s) {
        List<String> ret = new ArrayList<String>();
        int i = 0;
        while(i < s.length()) {
            int slash = s.indexOf('/', i);
            int size = Integer.valueOf(s.substring(i, slash));
            ret.add(s.substring(slash + 1, slash + size + 1));
            i = slash + size + 1;
        }
        return ret;
    }