Nicksxs's Blog

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public boolean isPalindrome(ListNode head) {
        if (head == null) {
            return true;
        }
        ListNode tail = head;
        LinkedList<Integer> stack = new LinkedList<>();
        // 循环入栈
        while (tail != null) {
            stack.push(tail.val);
            tail = tail.next;
        }
        // 再遍历链表跟出栈的对比，其实就是正反序的对比
        while (!stack.isEmpty()) {
            if (stack.peekFirst() == head.val) {
                stack.pollFirst();
                head = head.next;
            } else {
                return false;
            }
        }
        return true;

//        return stack.isEmpty();
    }
}

@Override
  protected void processField(Object bean, String beanName, Field field) {
    // register @Value on field
    Value value = field.getAnnotation(Value.class);
    if (value == null) {
      return;
    }
    Set<String> keys = placeholderHelper.extractPlaceholderKeys(value.value());

    if (keys.isEmpty()) {
      return;
    }

    for (String key : keys) {
      SpringValue springValue = new SpringValue(key, value.value(), bean, beanName, field, false);
      springValueRegistry.register(beanFactory, key, springValue);
      logger.debug("Monitoring {}", springValue);
    }
  }

public class SpringValueRegistry {
  private static final long CLEAN_INTERVAL_IN_SECONDS = 5;
  private final Map<BeanFactory, Multimap<String, SpringValue>> registry = Maps.newConcurrentMap();
  private final AtomicBoolean initialized = new AtomicBoolean(false);
  private final Object LOCK = new Object();

  public void register(BeanFactory beanFactory, String key, SpringValue springValue) {
    if (!registry.containsKey(beanFactory)) {
      synchronized (LOCK) {
        if (!registry.containsKey(beanFactory)) {
          registry.put(beanFactory, LinkedListMultimap.<String, SpringValue>create());
        }
      }
    }

    registry.get(beanFactory).put(key, springValue);

    // lazy initialize
    if (initialized.compareAndSet(false, true)) {
      initialize();
    }
  }

@Override
 public void onChange(ConfigChangeEvent changeEvent) {
   Set<String> keys = changeEvent.changedKeys();
   if (CollectionUtils.isEmpty(keys)) {
     return;
   }
   for (String key : keys) {
     // 1. check whether the changed key is relevant
     Collection<SpringValue> targetValues = springValueRegistry.get(beanFactory, key);
     if (targetValues == null || targetValues.isEmpty()) {
       continue;
     }

     // 2. check whether the value is really changed or not (since spring property sources have hierarchies)
     // 这里其实有一点比较绕，是因为 Apollo 里的 namespace 划分，会出现 key 相同，但是 namespace 不同的情况，所以会有个优先级存在，所以需要去校验 environment 里面的是否已经更新，如果未更新则表示不需要更新
     if (!shouldTriggerAutoUpdate(changeEvent, key)) {
       continue;
     }

     // 3. update the value
     for (SpringValue val : targetValues) {
       updateSpringValue(val);
     }
   }
 }

// 主体是个递归的应用
public int maxDepth(TreeNode root) {
    // 节点的退出条件之一
    if (root == null) {
        return 0;
    }
    int left = 0;
    int right = 0;
    // 存在左子树，就递归左子树
    if (root.left != null) {
        left = maxDepth(root.left);
    }
    // 存在右子树，就递归右子树
    if (root.right != null) {
        right = maxDepth(root.right);
    }
    // 前面返回后，左右取大者
    return Math.max(left + 1, right + 1);
}