1、层次遍历
public static ArrayList cengci(TreeNode root){
ArrayDeque queue = new ArrayDeque();
queue.add(root);
ArrayList result = new ArrayList();
while(queue.size()!= 0){
ArrayList single = new ArrayList();
int size. = queue.size();
for(int i = 0;i
TreeNode temp = queue.pop();
single.add(temp);
if(temp.left != null){
queue.add(temp.left);
}
if(temp.right != null){
queue.add(temp.right);
}
}
result.add(single);
}
return result;
}
2、交换左右节点
public static TreeNode jiaohuan(TreeNode root)){
if (root === null){
return null;
}
TreeNode left = jiaohuan(root.left);
TreeNode right = jiaohuan(root.right);
root.left = right;
root.right = left;
return root;
}
3、二叉树最大深度
public static int maxdep(TreeNode root){
if(root == null){
return 0;
}
int left = maxdep(root.left);
int right = maxdep(root.right);
return Math.max(left,right) +1;
}
4、某个路径和等于指定target
public static ArrayList result = new ArrayList();
public static ArrayList targersum(TreeNode root,int target){
back(root,target,new ArrayList);
return result;
}
public static void back(TreeNode root,int target,ArrayList path){
if (root == null){
return ;
}
path.add(root.val);
target = target - root.val;
if(target == 0 && root.left == null && root.right == null){
result.add(new ArrayList(path));
}
back(root.left,target,path);
back(root.right,target,path);
path.remove(path.size()-1);
}
5、二叉搜索树的公共祖先
public static TreeNode zuxian(TreeNode root ,TreeNode s1, TreeNode s2,){
if (root.val >=s2.val && root.val <=s1.val){
return root;
}
if(root.val >s2.val && root.val>s1.val){
return zuxian(root.right, s1,s2);
}else{
return zuxian(root.left, s1,s2);
}
}
6、二叉树公共祖先
public static TreeNode zuxian(TreeNode root ,TreeNode s1, TreeNode s2,){
if (root == null || s1.val == root.val || s2.val == root.val){
return root;
}
TreeNode left = zuxian(root.left,s1,s2);
TreeNode right = zuxian(root.right,s1,s2);
if (left != null && right != null){
return root;
}
return left ?right == null :right;
}
