Added Top Interview Questions ✅

Author: Jatin-8898

Top Interview Questions/Easy/ClimbingStairs.java

@@ -0,0 +1,23 @@
+class Solution {
+    public int climbStairs(int n) {
+        
+        int[] dp = new int[n + 1];
+        if (n == 1) {
+            return 1;
+        }
+        if (n == 2) {
+            return 2;
+        }
+        dp[0] = 0;
+        dp[1] = 1;
+        dp[2] = 2;
+        
+        for (int i = 3; i <= n; i++) {
+          dp[i] = dp[i-1] + dp[i - 2];
+        }
+        
+        return dp[n];
+
+        
+    }
+}

Top Interview Questions/Easy/CountAndSay.class

@@ -0,0 +1,33 @@
+class CountAndSay {
+    public static void main(String[] args) {
+        System.out.println(countAndSay(3));
+    }
+
+    public  static String countAndSay(int n) {// Eg 3 ie 21
+        
+        String s = "1";
+        
+        for (int i = 1; i < n; i++) {
+        
+            StringBuilder sb = new StringBuilder();
+            
+            for (int j = 1, count = 1;    j <= s.length();   j++) {
+            
+                if (j == s.length() || s.charAt(j - 1) != s.charAt(j)) {
+                    
+                    //System.out.println("IN IF " + s + " SB " +sb);
+                    sb.append(count);
+                    sb.append(s.charAt(j - 1));
+                    count = 1;
+                    //System.out.println("IN IF END " + s + " SB: " +sb + " co: "+count);
+                
+                } else {
+                    count++;
+                }
+            }
+            
+            s = sb.toString();
+        }
+        return s;
+    }
+}

Top Interview Questions/Easy/CountAndSay.java

@@ -0,0 +1,21 @@
+class Solution {
+    public int countPrimes(int n) {
+        
+        boolean[] notPrime = new boolean[n];    //Initially everything is false
+        int count = 0;
+        
+        for (int i = 2; i < n; i++) {//Eg 10
+        
+            if (notPrime[i] == false) { //2 is prime incr count
+                count++;
+            
+                for (int j = 2; i*j < n; j++) { //For 2 4 6 8 marks as NotPrime
+                    notPrime[i*j] = true;
+                }
+            }
+        }
+        
+        return count;
+        
+    }
+}

Top Interview Questions/Easy/CountPrimes.java

@@ -0,0 +1,10 @@
+class Solution{
+    
+    public int trailingZero(int n) { //Eg 25
+    
+        return n == 0   ? 0 :    (n/2 +  trailingZero(n/2));
+        
+        //25/2 = 5 + (25/2)     =>    5 + 1 = 6
+    
+    }
+}

Top Interview Questions/Easy/FactorialTrailingZero.java

@@ -0,0 +1,14 @@
+class Solution {
+    public int firstUniqChar(String s) {
+        int freq [] = new int[26];
+        
+        for(int i = 0; i < s.length(); i ++)
+            freq [s.charAt(i) - 'a'] ++;
+        
+        for(int i = 0; i < s.length(); i ++)
+            if(freq [s.charAt(i) - 'a'] == 1)
+                return i;
+        
+        return -1;
+    }
+}

Top Interview Questions/Easy/FirstUniqueChar.java

@@ -0,0 +1,31 @@
+import java.util.*;
+class FizzBuzz {
+
+    public List<String> fizzBuzz(int n) {
+        List<String> list = new ArrayList<String>(n);
+        
+        for(int i=1, fizz=0, buzz=0;  i<=n ;i++){
+            
+            fizz++;
+            buzz++;
+            
+            if(fizz==3 && buzz==5){
+                list.add("FizzBuzz");
+                fizz=0;
+                buzz=0;
+            
+            }else if(fizz==3){
+                list.add("Fizz");
+                fizz=0;
+            
+            }else if(buzz==5){
+                list.add("Buzz");
+                buzz=0;
+            
+            }else{
+                list.add(String.valueOf(i));
+            }
+        } 
+        return list;
+    }
+}

Top Interview Questions/Easy/FizzBuzz.java

@@ -0,0 +1,47 @@
+import java.util.*;
+class HappyNumber {
+    public static void main(String[] args) {
+        isHappy(19);
+    }
+    public static boolean isHappy(int n) {
+        
+        if(n < 10) {
+            
+		    if(n==1||n==7) 
+                return true;
+		    else 
+                return false;
+	    }
+        
+        int b;
+        int sum=0;
+        
+        while(n > 0) {
+              b = n % 10;
+              sum = sum + b*b; 
+              n = n / 10;
+        } 
+        
+         return isHappy(sum);
+    }
+
+
+    /* ANNOTHER SOLUTION */
+    public boolean isHappy2(int n) {
+        Set<Integer> set = new HashSet<>();
+        while(getSquareSum(n) != 1){
+             n = getSquareSum(n);
+            if(!set.add(n))return false; 
+        }
+        return true;
+    }
+    
+    private int getSquareSum(int n){
+        int result = 0;
+        while(n != 0){
+            result += Math.pow(n%10,2); 
+            n = n/10;
+        }
+        return result; 
+    }
+}

Top Interview Questions/Easy/HappyNumber.class

@@ -0,0 +1,37 @@
+class Solution {
+    
+    public int rob(int[] nums) {    //Eg 2, 7 ,9 ,3 ,1 
+
+        int n = nums.length;        //n=5
+        
+        if (n == 0) return 0;
+        
+        if (n == 1) return nums[0];
+        
+        if (n > 2)                          //9+2 = 11
+            nums[2] += nums[0];             //Arr becomes 2 7 11 3 1
+        
+
+        for (int i = 3; i < n; i++)             //num[3] = 3 + Max(7,2) => 10,   Arr [2 7 11 10 1]
+            nums[i] += Math.max(nums[i-2], nums[i-3]);  //num[4] = 1 + Max(11,7) =>  12
+        
+
+        return Math.max(nums[n-1], nums[n-2]);  //Max(12,10)  => return 12 correct ans
+    }
+
+    /* ANOTHER APPROACH */
+    public int rob2(int[] nums) {
+        if (nums.length == 0) return 0;
+        
+        int[] memo = new int[nums.length + 1];
+        memo[0] = 0;
+        memo[1] = nums[0];
+        
+        for (int i = 1; i < nums.length; i++) {
+            int val = nums[i];
+            memo[i+1] = Math.max(memo[i], memo[i-1] + val);
+        }
+        
+        return memo[nums.length];
+    }
+}