637. Average of Levels in Binary Tree\633. Sum of Square Numbers\643. Maximum Average Subarray I

637. Average of Levels in Binary Tree

Problem

Given a non-empty binary tree, return the average value of the nodes on each level in the form of an array.

Example 1:

Input:    3   / \  9  20    /  \   15   7Output: [3, 14.5, 11]Explanation:The average value of nodes on level 0 is 3,  on level 1 is 14.5, and on level 2 is 11. Hence return [3, 14.5, 11].

Note:
The range of node’s value is in the range of 32-bit signed integer.

Implementation

Use BFS to solve this problem.

/** * 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<double> averageOfLevels(TreeNode* root) {        vector<double> res;        queue<TreeNode*> que;        if(root)            que.push(root);        else             return res;        while(!que.empty()) {            int sz = que.size();            double level_sum = 0;            for(int idx = 0; idx < sz; idx++) {                TreeNode* tp = que.front();                que.pop();                level_sum += tp->val;                if(tp->left)                    que.push(tp->left);                if(tp->right)                    que.push(tp->right);            }                res.push_back(level_sum/sz);        }               return res;    }};

633. Sum of Square Numbers

Problem Description

Given a non-negative integer c, your task is to decide whether there’re two integers a and b such that a2 + b2 = c.

Example 1:

Input: 5Output: TrueExplanation: 1 * 1 + 2 * 2 = 5Example 2:Input: 3Output: False

Implementation

class Solution {public:    bool judgeSquareSum(int c) {        int end_ele = ceil(sqrt(c));        int stt_ele = floor(sqrt(c/2.0));        for(int idx = end_ele; idx >= stt_ele; idx--) {            int left = c - idx*idx;            if(ceil(sqrt(left)) == floor(sqrt(left))) {                return true;            }            }            return false;    }};

643. Maximum Average Subarray I

Description

Given an array consisting of n integers, find the contiguous subarray of given length k that has the maximum average value. And you need to output the maximum average value.

Example 1:

Input: [1,12,-5,-6,50,3], k = 4Output: 12.75Explanation: Maximum average is (12-5-6+50)/4 = 51/4 = 12.75

Note:
1 <= k <= n <= 30,000.
Elements of the given array will be in the range [-10,000, 10,000].

Implementation

class Solution {public:    double findMaxAverage(vector<int>& nums, int k) {        int size = nums.size();        int res = 0;        if(size < k || k == 0) {            return res;        }            for(int idx = 1; idx < size; idx++) {            nums[idx] += nums[idx-1];        }           res = nums[k-1];        for(int idx = k; idx < size; idx++) {            if(nums[idx]-nums[idx-k]> res) {                res = nums[idx] - nums[idx-k];            }        }            return double(res)/k;    }};