Find Largest Value in Each Tree Row

You need to find the largest value in each row of a binary tree.

解析

找到每一層的最大節點值。

解法1：層序遍歷

直接層次遍歷每一層，獲得最大值。

class Solution {
public:
    vector<int> largestValues(TreeNode* root) {
        vector<int> res;
        if(!root) return res;
        queue
 
<TreeNode*> q;
        q.push(root);
        while(!q.empty()){
            int size = q.size();
            int m = INT_MIN;
            for(int i=0;i<size;i++){
                TreeNode* p = q.front();
                q.pop();
                m = max(m, p->val);
                if(p->left) q.push(p->left);
                if
 
(p->right) q.push(p->right);
            }
            res.push_back(m);
        }
        return res;
    }
};

解法2：遞迴，DFS

深度搜索樹，當res大小等於深度時，增加res節點，當小於時，直接比較取最大值。

class Solution {
public:
    vector<int> largestValues(TreeNode* root) {
        vector<int> res;
        DFS(root, 0
 
, res);
        return res;
    }
    void DFS(TreeNode* root, int level, vector<int>& res){
        if(!root) return;
        if(res.size() == level)
            res.push_back(root->val);
        else
            res[level] = max(res[level], root->val);
        DFS(root->left, level+1, res);
        DFS(root->right, level+1, res);
    }
};

參考

http://www.cnblogs.com/grandyang/p/6417826.html