Sum Root to Leaf Numbers

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問題：根節點到葉子結點的所有權值和
分析：從根節點遍曆，若遍曆到葉子結點，則sum+其路徑的所有權值和

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    int sum;    void dfs(TreeNode *root,int num)    {        if(root->left==NULL && root->right==NULL) sum+=num;        if(root->left) dfs(root->left,num*10+root->left->val);        if(root->right) dfs(root->right,num*10+root->right->val);    }    int sumNumbers(TreeNode *root) {        if(root==NULL) return 0;        sum=0;        int num=0;        dfs(root,root->val);        return sum;    }};