力扣 深度优先搜索 199. 二叉树的右视图
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
List<Integer> result = new ArrayList<>();
public List<Integer> rightSideView(TreeNode root) {
dfs(root,0);
return result;
}
public void dfs(TreeNode node,int depth){
// 如果当前深度比size大，加入到result；
if(depth > result.size()){
result.add(node.val);
}
else{
// 如果当前深度<= size，将当前result深度的值设为当前值；
// 这里代码主要和下发的dfs联动，因为是先dfs left，所以再dfs right时会更新数据
// 最后生成右视图 结果
// 反之，生成左视图结果只需先dfs right，再dfs left
result.set(depth,node.val);
}
dfs(root.left,depth+1);
dfs(root.right,depth+1);
}
}
bfs
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode() {}
* TreeNode(int val) { this.val = val; }
* TreeNode(int val, TreeNode left, TreeNode right) {
* this.val = val;
* this.left = left;
* this.right = right;
* }
* }
*/
class Solution {
public List<Integer> rightSideView(TreeNode root) {
List<Integer> result = new ArrayList<>();
if (root == null)
return result;
Queue<TreeNode> queue = new LinkedList<>();
queue.offer(root);
int size;
while (!queue.isEmpty()) {
size = queue.size();
for (int i = 0; i < size; i++) {
TreeNode temp = queue.poll();
if (temp.left != null)
queue.offer(temp.left);
if (temp.right != null)
queue.offer(temp.right);
if (i == size - 1)
result.add(temp.val);
}
}
return result;
}
}
