129 Sum Root to Leaf Numbers

129 Sum Root to Leaf Numbers


https://leetcode.com/problems/sum-root-to-leaf-numbers/discuss/41363/Short-Java-solution.-Recursion.



不是自己写的， tree 的 recursion 做的 不好
class Solution {
    public int sumNumbers(TreeNode root) {
      return sum(root, 0);
    }
    private int sum(TreeNode n, int prev){
      if(n == null){
        return 0;
      }
      if(n.right == null && n.left == null){
        return prev * 10 + n.val;
      }
      int left = sum(n.left, prev * 10 + n.val);
      int right = sum(n.right, prev * 10 + n.val);
      int sum = left + right;
      return sum;
        
    }
}