Tip3(Easy)

문제 : https://leetcode.com/problems/sum-of-root-to-leaf-binary-numbers/submissions/

참고 : https://leetcode.com/problems/sum-of-root-to-leaf-binary-numbers/discuss/455682/Java-100-time-and-memory-Bit-Operations-(concise)

List<String> bsArray = new ArrayList<>();
public int sumRootToLeaf(TreeNode root) {
	StringBuilder sb = new StringBuilder();
	sum(root, sb);
	int ans = 0;
	for(String s : bsArray) {
		ans += Integer.parseInt(s, 2);
	}
	return ans;
}

void sum(TreeNode node, StringBuilder bs) {
	if(node != null) {
		bs.append(node.val);
		if(node.left == null & node.right == null) {
			bsArray.add(bs.toString());
		}
		sum(node.left, bs);
		sum(node.right, bs);
		if(bs.length() > 0) {
			bs.deleteCharAt(bs.length() - 1);
		}
	}
}

별로 좋은 코드는 아니다

 

좋은 재귀 연습 문제

https://leetcode.com/problems/maximum-depth-of-binary-tree/

https://leetcode.com/problems/maximum-depth-of-binary-tree/discuss/522890/Java-100-2-lines

int max = 0;

public int maxDepth(TreeNode root) {
	dfs(root, 0);
	return max;
}

public void dfs(TreeNode node, int depth) {
	if(node != null) {
		depth++;
		if(depth > max) max = depth;
		dfs(node.left, depth);
		dfs(node.right, depth);
	}
}

연결된 문제

https://leetcode.com/problems/maximum-depth-of-n-ary-tree/

public int maxDepth(Node root) {
	if (root == null) return 0;
	int max = 0;
	for(Node n : root.children) {
		int temp = maxDepth(n);
		if(temp > max) max = temp;
	}
	return max + 1;
}