LeetCode部分题解

LeetCode Algorithm部分.515

【515】 Find Bottom Left Tree Value

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

Example:

Input:

     1
    / \
   3   2
  / \   \  
 5   3   9 

Output: [1, 3, 9]

该题的题意为寻找树的每层节点的最大值，依然用的是层遍历。下面是实现

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<int> largestValues(TreeNode* root) {
        vector<int> answer;
        vector<TreeNode*> nq;
        if(root==NULL) return answer;
        else if(root->left == NULL && root->right == NULL) answer.push_back(root->val);
        else{
            answer.push_back(root->val);
            if(root->left != NULL) nq.push_back(root->left);
            if(root->right != NULL) nq.push_back(root->right);
        }
        while(!nq.empty()){
            int max1 = nq[0]->val;
            vector<TreeNode*> tem;
            for(int i = 0; i < nq.size(); i++){
                max1 = max(nq[i]->val, max1);
                if(nq[i]->left != NULL) tem.push_back(nq[i]->left);
                if(nq[i]->right != NULL) tem.push_back(nq[i]->right);
            }
            answer.push_back(max1);
            nq = tem;
        }
        return answer;
    }
};