Java日记2018-06-05
2018-06-05 本文已影响0人
hayes0420
- 二叉树中和为某一值的路径
递归的实现,栈弹入弹出的时机选择还蛮妙,测试数据时候猜测+试验出来,理解了一下结果
//二叉树中和为某一值的路径
public static void findpath(TreeNode root, int target) {
if (root == null)
return;
Stack<Integer> path = new Stack<Integer>();
findpathcore(root, target, path);
}
public static void findpathcore(TreeNode root, int target, Stack<Integer> path) {
if (root == null)
return;
//注意push即pop的位置,要在判断外边,这样弹出时候能弹出到最外层,蛮抽象,再看时候可能会更理解……
path.push(root.val);
if (root.left == null && root.right == null) {
if (target == root.val) {
//path.push(root.val);
for (int i : path) {
System.out.print(i + " ");
}
System.out.println(" ");
}
} else {
//path.push(root.val);
findpathcore(root.left, target - root.val, path);
findpathcore(root.right, target - root.val, path);
//path.pop();
}
path.pop();
}
- 复杂链表的复制
方法还是赋值拆分的老路
直接用题解的方法,主要看看下次能不能更快速想到这个方法
public RandomListNode Clone(RandomListNode pHead) {
if (pHead == null)
return null;
// 插入新节点
RandomListNode cur = pHead;
while (cur != null) {
RandomListNode clone = new RandomListNode(cur.label);
clone.next = cur.next;
cur.next = clone;
cur = clone.next;
}
// 建立 random 链接
cur = pHead;
while (cur != null) {
RandomListNode clone = cur.next;
if (cur.random != null)
clone.random = cur.random.next;
cur = clone.next;
}
// 拆分
cur = pHead;
RandomListNode pCloneHead = pHead.next;
while (cur.next != null) {
RandomListNode next = cur.next;
cur.next = next.next;
cur = next;
}
return pCloneHead;
}
- 二叉搜索树与双向链表
原来的做法是错误的,需要重新审视
private TreeNode pre = null;
private TreeNode head = null;
public TreeNode Convert(TreeNode root) {
if (root == null)
return null;
inOrder(root);
return head;
}
private void inOrder(TreeNode node) {
if (node == null)
return;
inOrder(node.left);
node.left = pre;
if (pre != null)
pre.right = node;
pre = node;
if (head == null)
head = node;
inOrder(node.right);
}