Added Amazon Coding Interview Questions

Amazon_Interview_Questions/Easy/Convert_Sorted_Array_to_ Binary_Search_Tree.cpp

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+/*
+
+	Problem Link: https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/
+
+*/
+
+	/**
+	 * Definition for a binary tree node.
+	 * struct TreeNode {
+	 *     int val;
+	 *     TreeNode *left;
+	 *     TreeNode *right;
+	 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
+	 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
+	 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
+	 * };
+	 */
+	class Solution {
+	public:
+
+	    TreeNode *MakeBst(vector<int>&nums, int low, int high){
+	        if(low > high)
+	            return NULL;
+	        int middle = low + (high-low)/2;
+	        TreeNode *root = new TreeNode(nums[middle]);
+	        root -> left = MakeBst(nums,low,middle-1);
+	        root -> right = MakeBst(nums,middle+1,high);
+	        return root;
+	    }
+
+	    TreeNode* sortedArrayToBST(vector<int>& nums) {
+	        if(nums.size()==0)
+	            return NULL;
+	        return MakeBst(nums,0,int(nums.size())-1);
+	    }
+	}; 

Amazon_Interview_Questions/Easy/Fizz_Buzz.cpp

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+/*
+
+	Problem Link: https://leetcode.com/problems/fizz-buzz/
+
+*/
+
+class Solution {
+public:
+    vector<string> fizzBuzz(int n) {
+        vector<string>s;
+      for(int i=1 ; i<=n ;i++){
+        if(i%3==0 && i%5!=0){
+          s.push_back("Fizz");
+        }
+        else if(i%3!=0 && i%5==0){
+          s.push_back("Buzz");
+        }
+        else if(i%3==0 && i%5==0){
+          s.push_back("FizzBuzz");
+        }
+        else{          
+          s.push_back(std::to_string(i));
+        }
+      }
+      return s;
+    }
+};

Amazon_Interview_Questions/Easy/Lemonade_Change.cpp

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+/*
+
+	Problem Link: https://leetcode.com/problems/lemonade-change/
+
+*/
+
+
+class Solution {
+public:
+    bool lemonadeChange(vector<int>& bills) {
+        int n = bills.size();
+        if(bills[0]==10)
+            return false;
+        int five=0, ten=0;
+        for(int i=0; i<n; i++){
+            if(bills[i]==5)
+                five += 1;
+            else if(bills[i]==10){
+                ten += 1;
+                five -= 1;
+            }
+            else if(ten > 0){
+                ten -= 1;
+                five -= 1;
+            }
+            else
+                five -= 3;
+            if(five < 0)
+                return false;
+        }
+        return true;
+    }
+};

Amazon_Interview_Questions/Easy/Sqrt(x).cpp

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+/*
+
+	Problem Link: https://leetcode.com/problems/sqrtx/
+
+*/
+
+
+class Solution {
+public:
+    int mySqrt(int x) {
+       if(x==0) return 0;
+        int l=0, r=x;
+
+        int res, mid;  //binary search
+     while(l<=r){             
+            mid=(l+r)/2;
+         if(mid == 0) return 1;
+            if(mid==x/mid) return mid;    
+            else if(mid<x/mid){             
+                l=mid+1;       
+                res = mid;      
+            }
+            else r=mid-1;       
+        }
+        return res; 
+    }
+};

Amazon_Interview_Questions/Medium/House_Robber.cpp

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+/*
+
+	Problem Link: https://leetcode.com/problems/house-robber/
+
+*/
+
+class Solution {
+public:
+    int rob(vector<int>& nums) {
+        int n = nums.size();
+        if(n==0)
+            return 0;
+        vector<int>a(n);
+        if(n>=1)
+            a[0] = nums[0];
+        if(n>=2)
+            a[1] = max(nums[0],nums[1]);
+        for(int i=2; i<n; i++){
+            a[i] = max(a[i-1],a[i-2]+nums[i]);
+        }
+        return a[n-1];
+    }
+};

Amazon_Interview_Questions/Medium/Maximum_Product_Subarray.cpp

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+/*
+
+	Problem Link: https://leetcode.com/problems/maximum-product-subarray/
+
+*/
+
+class Solution {
+public:
+    int maxProduct(vector<int>& nums) {
+        if(nums.size()==0)
+            return 0;
+        int maxSub = nums[0];
+        int minSub = nums[0];
+        int maxProd = nums[0];
+        for(int i=1; i<nums.size(); i++){
+           /* when element is negative we do swap because 
+			when multiplying with a negative integer, number becomes positive so minimum negative numebr will become the maximum number
+			*/
+            if(nums[i]<0)
+                swap(maxSub, minSub);
+            maxSub = max(maxSub*nums[i],nums[i]);
+            minSub = min(minSub*nums[i],nums[i]);
+            maxProd = max(maxProd,maxSub);
+        }
+        return maxProd;
+    }
+};

Amazon_Interview_Questions/Medium/Perfect_Squares.cpp

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+/*
+
+	Problem Link: https://leetcode.com/problems/perfect-squares/
+
+*/
+
+class Solution {
+public:
+    int numSquares(int n) {
+        if(ceil(sqrt(n)) == floor(sqrt(n))) 
+            return 1;
+        //legendre's 3-square theorem
+        while(n%4==0)
+            n/=4;
+        if(n%8==7)
+            return 4;
+        for(int i=1; i*i<=n; i++){
+            int base = sqrt(n-i*i);
+            if(base * base == (n-i*i))
+                return 2;
+        }
+        return 3;
+    }
+};