Main56.java

package JZOfferTuJi;

import java.util.ArrayDeque;
import java.util.HashSet;
import java.util.Queue;
import java.util.Set;

// 深度优先遍历
public class Main56 {
    Set<Integer> set = new HashSet<>();
    public boolean findTarget(TreeNode root, int k) {
        if(root == null) {
            return false;
        }
        if(set.contains(k - root.val)) {
            return true;
        }
        set.add(root.val);
        return findTarget(root.left, k) || findTarget(root.right, k);
    }
}

// 广度优先遍历
class Main56_1 {
    public boolean findTarget(TreeNode root, int k) {
        Set<Integer> set = new HashSet<>();
        Queue<TreeNode> queue = new ArrayDeque<>();
        queue.offer(root);
        while (!queue.isEmpty()) {
            TreeNode temp = queue.poll();
            if(set.contains(k - temp.val)) {
                return true;
            }
            set.add(temp.val);
            if(temp.left != null) {
                queue.add(temp.left);
            }
            if(temp.right != null) {
                queue.add(temp.right);
            }
        }
        return false;
    }
}