[leetcode]Sum Root to Leaf Numbers

原创于 2015-03-17 19:32:00 发布 · 305 阅读

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本文介绍了一种算法，用于求解给定二叉树中所有从根节点到叶子节点路径数字之和的问题。通过深度优先搜索（DFS）遍历二叉树，将每条路径上的数字累加得到总和。

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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.

DFS

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<int> st;
    int ans = 0;
    int sumNumbers(TreeNode *root) {
        if(root==NULL) return ans;
        st.push_back(root->val);
        if(root->left==NULL&&root->right==NULL){
            int a = 0;
            int size = st.size();
            for(int i=0;i<size;i++){
                 a*=10;
                 a+=st[i];
            }
            ans += a;
            return ans;
        }
        //return sumNumbers(root->left)+sumNumbers(root->right);
        sumNumbers(root->left);
        if(root->left !=NULL) st.erase(st.end()-1);
        sumNumbers(root->right);
        if(root->right !=NULL) st.erase(st.end()-1);
        return ans;
    }
};