public String reverseLeftWords(String s, int n) {
        char[] chars = s.toCharArray();
        int length = chars.length;
        int t = n;
        for (int i = 0; i <  n; i++) {
            n--;
            char temp = chars[i];
            chars[i] = chars[n];
            chars[n] = temp;
        }
        for (int i = t; i < length; i++) {
            char temp = chars[i];
            chars[i] = chars[length - 1];
            chars[length - 1] = temp;
            length--;
        }
        length = chars.length;
        for (int i = 0; i < length; i++) {
            char temp = chars[i];
            chars[i] = chars[length - 1];
            chars[length - 1] = temp;
            length--;
        }
        return String.valueOf(chars);
    }
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public static int strStr(String haystack, String needle) {
    char[] chars = haystack.toCharArray();
    char[] chars1 = needle.toCharArray();
    for (int i = 0; i < chars.length; i++) {
        int n = 0;
        int m = i;
        while(m < chars.length && n < chars1.length && chars[m] == chars1[n]){
            m++;
            n++;
        }
        if (n == chars1.length && chars[m - 1] == chars1[n - 1]){
            return i;
        }
    }
    return -1;
}
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public boolean repeatedSubstringPattern(String s) {
        if (s.equals("")) return false;
        int len = s.length();
        // 原串加个空格(哨兵)，使下标从1开始，这样j从0开始，也不用初始化了
        s = " " + s;
        char[] chars = s.toCharArray();
        int[] next = new int[len + 1];
        // 构造 next 数组过程，j从0开始(空格)，i从2开始
        for (int i = 2, j = 0; i <= len; i++) {
            // 匹配不成功，j回到前一位置 next 数组所对应的值
            while (j > 0 && chars[i] != chars[j + 1]) j = next[j];
            // 匹配成功，j往后移
            if (chars[i] == chars[j + 1]) j++;
            // 更新 next 数组的值
            next[i] = j;
        }
        // 最后判断是否是重复的子字符串，这里 next[len] 即代表next数组末尾的值
        if (next[len] > 0 && len % (len - next[len]) == 0) {
            return true;
        }
        return false;
    }
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public class MyStack {
    Queue<Integer> inQueue ;
    Queue<Integer> outQueue ;
    public MyStack() {
        inQueue = new LinkedList<>();
        outQueue = new LinkedList<>();
    }
    public void push(int x) {
        outQueue.offer(x);
        while(!inQueue.isEmpty()){
            outQueue.offer(inQueue.poll());
        }
        Queue<Integer> temp ;
        temp = inQueue;
        inQueue = outQueue;
        outQueue = temp;
    }
    public int pop() {
        return inQueue.poll();
    }
    public int top() {
        return inQueue.peek();
    }
    public boolean empty() {
        return inQueue.isEmpty();
    }
}
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public boolean isValid(String s) {
        Deque<Character> deque = new LinkedList<>();
        char ch;
        for (int i = 0; i < s.length(); i++) {
            ch = s.charAt(i);
            //碰到左括号，就把相应的右括号入栈
            if (ch == '(') {
                deque.push(')');
            }else if (ch == '{') {
                deque.push('}');
            }else if (ch == '[') {
                deque.push(']');
            // 栈为空或者栈顶元素与当前 ch不匹配，则返回 false
            } else if (deque.isEmpty() || deque.peek() != ch) { 
                return false;
            }else {
                // 栈不为空，且栈顶元素与 ch一致
                deque.pop();
            }
        }
        //最后判断栈中元素是否匹配
        return deque.isEmpty();
    }
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