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.
题解：
类似于 Path Sum 和 Path Sum II，迭代方法依然是后序遍历的思路，先遍历左右孩子。
Solution 1
1 class Solution { 2 public: 3 int sumNumbers(TreeNode* root) { 4 if (!root) 5 return 0; 6 return dfs(root, 0); 7 } 8 int dfs(TreeNode* root, int sum) { 9 if (!root) 10 return 0; 11 sum = sum * 10 + root->val; 12 if (!root->left && !root->right) 13 return sum; 14 return dfs(root->left, sum) + dfs(root->right, sum); 15 } 16 };
Solution 2
1 class Solution { 2 public: 3 int sumNumbers(TreeNode* root) { 4 if (!root) 5 return 0; 6 queue<TreeNode*> q1; 7 queue<int> q2; 8 q1.push(root); 9 q2.push(root->val); 10 11 int sum = 0, cursum = 0; 12 TreeNode* cur = root; 13 14 while (!q1.empty()) { 15 cur = q1.front(); 16 cursum = q2.front(); 17 q1.pop(); 18 q2.pop(); 19 20 if (!cur->left && !cur->right) { 21 sum += cursum; 22 } 23 if (cur->left) { 24 q1.push(cur->left); 25 q2.push(cursum * 10 + cur->left->val); 26 } 27 if (cur->right) { 28 q1.push(cur->right); 29 q2.push(cursum * 10 + cur->right->val); 30 } 31 } 32 return sum; 33 } 34 };
Solution 3
1 class Solution { 2 public: 3 int sumNumbers(TreeNode* root) { 4 if (!root) 5 return 0; 6 stack<TreeNode*> s1; 7 stack<int> s2; 8 int sum = 0, cursum = 0; 9 TreeNode* cur = root, *pre = nullptr; 10 while (cur || !s1.empty()) { 11 while (cur) { 12 s1.push(cur); 13 cursum = cursum * 10 + cur->val; 14 s2.push(cursum); 15 cur = cur->left; 16 } 17 cur = s1.top(); 18 if (!cur->left && !cur->right) { 19 sum += cursum; 20 } 21 if (cur->right && cur->right != pre) { 22 cur = cur->right; 23 } else { 24 pre = cur; 25 s1.pop(); 26 cursum = s2.top(); 27 s2.pop(); 28 cursum -= cur->val; 29 cursum /= 10; 30 cur = nullptr; 31 } 32 } 33 return sum; 34 } 35 };