leetcode1302-层数最深叶子节点的和

层数最深叶子节点的和

• BFS

层序遍历树，返回最后一次计算的结果

class Solution {
    public int deepestLeavesSum(TreeNode root) {
        List<TreeNode> list = new ArrayList<>();
        int start = 0, end = 1, last = 1, cnt = 0;
        list.add(root);
        while(start < end){
            cnt = 0;
            while(start < last){
                TreeNode node = list.get(start++);
                cnt += node.val;
                if(node.left != null){
                    list.add(node.left);
                    end++;
                }
                if(node.right != null){
                    list.add(node.right);
                    end++;
                }
            }
            last = end;
        }
        return cnt;
    }
}

• DFS

维护最大的层数maxLevel和返回值sum。如果当前层数大于maxLevel，那么更新maxLevel，并将sum赋值为root.val。如果当前层数等于maxLevel，那么sum加上root.val

class Solution {
    int maxLevel = -1, sum = 0;
    public int deepestLeavesSum(TreeNode root) {
        dfs(root, 0);
        return sum;
    }
    public void dfs(TreeNode root, int level){
        if(root == null)    return;
        if(level > maxLevel){
            maxLevel = level;
            sum = root.val;
        }else if(level == maxLevel){
            sum += root.val;
        }
        dfs(root.left, level+1);
        dfs(root.right, level+1);
    }
}