129. Sum Root to Leaf Numbers
基本的dfs
1 int sum = 0; 2 3 public int sumNumbers(TreeNode root) { 4 if(root == null) { 5 return 0; 6 } 7 helper(root, 0); 8 return sum; 9 } 10 11 private void helper(TreeNode root, int curSum) { 12 if(root == null) { 13 return; 14 } 15 if(root.left == null && root.right == null) { 16 sum += curSum * 10 + root.val; 17 return; 18 } 19 helper(root.left, curSum * 10 + root.val); 20 helper(root.right, curSum * 10 + root.val); 21 }