剑指Offer之Java算法习题精讲二叉树与N叉树

class Solution {
    StringBuffer sb = new StringBuffer();
    List<String> list = new ArrayList<String>();
    public List<String> binaryTreePaths(TreeNode root) {
        method(root);
        return list;
    }
    public void method(TreeNode root){
        if(root==null) return;
        int t = sb.length();
        sb.append(root.val);
        if(root.left==null&&root.right==null){
            list.add(sb.toString());
        }
        sb.append("->");
        method(root.left);
        method(root.right);
        sb.delete(t, sb.length());
    }
}

class Solution {
    int ans = 0;
    public int sumOfLeftLeaves(TreeNode root) {
        method(root,false);
        return ans;
    }
    public void method(TreeNode root,boolean flag){
        if(root==null) return;
        if(root.left==null&&root.right==null&&flag){
            ans+=root.val;
            return;
        }
        method(root.left,true);
        method(root.right,false);
    }
}

 
class Solution {
    public int maxDepth(Node root) {
        if(root==null){
            return 0;
        }
        int maxChildDepth = 0;
        for(int i = 0;i<root.children.size();i++){
            int childDepth = maxDepth(root.children.get(i));
            maxChildDepth = Math.max(maxChildDepth, childDepth);
        }
        return maxChildDepth+1;
    }
}