All adjacent duplicate entries deleted string (leetcode1047) - Java

Topics requirements:

String S is given by the lowercase letters, delete duplicates and selects two identical letters adjacent to, and remove them
repeatedly performed in duplicate S delete, delete can not continue until
completion of all delete duplicates after returning final string. The only answer guarantee

Example:
Input: "abbaca"
Output: "ca"

solution

Method One: Use stack ideas

class Solution {
    public String removeDuplicates(String S) {
        if(S==null||S=="") return S;//特殊情况
        StringBuilder res=new StringBuilder();//栈
        int top=-1;//栈顶
        for(char c:S.toCharArray()){
            if(top==-1||res.charAt(top)!=c){//匹配不成功两种情况：栈为空，n不相等
                res.append(c);
                top++;
            }
            else{
                res.deleteCharAt(top);//已经匹配，删除改字符
                top--;
            }
        }
        return res.toString();
    }
}
/*
str.toCharArray()
sb.charAt()
sb.deleteCharAt()
*/

Method two: the original step algorithm (for cpp)

class Solution {
public:
    string removeDuplicates(string S) {
        int top = 0;
        for (char ch : S) {
            if (top == 0 || S[top - 1] != ch) {
                S[top++] = ch;
            } else {
                top--;
            }
        }
        S.resize(top);
        return S;
    }
};