week3-NO.515. Find Largest Value in Each Tree Row

题目

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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]

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https://leetcode.com/problems/find-largest-value-in-each-tree-row/?tab=Description

思路

题目需要找到数的每一层中值最大的点，即深度相同的点中值最大的点。

思路是使用一个数组保存每个深度的最大值，从根出发并遍历节点的时候，记录下走到该点时的深度，与数组中现有的最大值比较，并加上递归的思想。

源程序

/** * 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) {        int max[10000],i,maxdep = 0,dep = 0;        vector<int> res;        for(i = 0;i < 10000;i ++)            max[i] = -2147483648;        if(root){            dfs(res,root,dep,max,maxdep);            for(i = 0;i <= maxdep;i ++)                res.push_back(max[i]);        }        return res;    }    void dfs(vector<int>& res,TreeNode *root,int dep,int max[],int &maxdep){        if(root->val > max[dep])            max[dep] = root->val;        if(dep > maxdep)            maxdep = dep;                    if(root->left != NULL)            dfs(res,root->left,dep + 1,max,maxdep);        if(root->right != NULL)            dfs(res,root->right,dep + 1,max,maxdep);    }};