129. Sum Root to Leaf Numbers

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.

递归解法：

class Solution {
public:
    int sum=0;
    void find(TreeNode *root,int t){
        if(root->left==NULL&&root->right==NULL){
            sum+=t*10+root->val;
        }else{
            if(root->left!=NULL)
                find(root->left,t*10+root->val);
            if(root->right!=NULL)
                find(root->right,t*10+root->val);
        }
    }
    int sumNumbers(TreeNode* root) {
        if(root==NULL)return sum;
        else{
            find(root,0);
            return sum;
        }
    }
};

非递归：

class Solution {
public:
    int sumNumbers(TreeNode* root) {
        int sum=0,t=0;
        if(root==NULL)return sum;
        stack<TreeNode*>st;
        map<TreeNode*,bool>visit;
        st.push(root);
        visit[root]=true;
        t=root->val;
        while(!st.empty()){
            TreeNode *top=st.top();
            if(top->left!=NULL&&visit[top->left]==false){
                st.push(top->left);
                visit[top->left]=true;
                t=t*10+top->left->val;
                continue;
            }
            else if(top->right!=NULL&&visit[top->right]==false){
                st.push(top->right);
                visit[top->right]=true;
                t=t*10+top->right->val;
                continue;
            }
            else if(top->left==NULL&&top->right==NULL){
                sum+=t;
            }
            st.pop();
            t=t/10;
        }
        return sum;
    }
};