Given a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.
An example is the root-to-leaf path 1->2->3 which represents the number 123.
Find the total sum of all root-to-leaf numbers.
For example,
1
/ \
2 3
The root-to-leaf path 1->2 represents the number 12.
The root-to-leaf path 1->3 represents the number 13.
Return the sum = 12 + 13 = 25.
Solution1：
思路：Recursive[递归post-order dfs来upwards累积]，并上面的sum 调用时downwards向下传递
Time Complexity: O(N) Space Complexity: O(N) 递归缓存
Solution2：
思路： 全局g_sum, dfs更新
Solution1 Code：
class Solution {
public int sumNumbers(TreeNode root) {
return dfsSum(root, 0);
}
private int dfsSum(TreeNode node, int cur_sum) {
if(node == null) return 0;
if(node.left == null && node.right == null) return cur_sum * 10 + node.val;
int sum = dfsSum(node.left, cur_sum * 10 + node.val) + dfsSum(node.right, cur_sum * 10 + node.val);
return sum;
}
}
Solution2 Code：
class Solution {
private int g_sum = 0;
public int sumNumbers(TreeNode root) {
dfsSum(root, 0);
return g_sum;
}
private void dfsSum(TreeNode node, int cur_sum) {
if(node == null) return;
if(node.left == null && node.right == null) {
g_sum += (cur_sum * 10 + node.val);
}
dfsSum(node.left, cur_sum * 10 + node.val);
dfsSum(node.right, cur_sum * 10 + node.val);
}
}
