Blind75 Problems in java

DuplicateInList.java

import java.util.HashSet; 

class DuplicateInList {
    
    public static boolean doDuplicateExists(int[] arr){
        HashSet<Integer> numbers = new HashSet<Integer>();
        
        for(int i=0; i<arr.length; i++){
            if(numbers.contains(arr[i])){
                return true;
            }
            numbers.add(arr[i]);
        }
        
        return false;
    }
    
    
    
    public static void main(String[] args) {
        int[] arr = {7, 1, 5, 3, 6, 4};

        System.out.println(doDuplicateExists(arr));
    }
}

DuplicateInListUsingFloyds.java

public int findDuplicate(int[] nums) {
    int slow = nums[0];
    int fast = nums[0];

    do {
        slow = nums[slow];
        fast = nums[nums[fast]];
    } while (slow != fast);

    slow = nums[0];

    while(slow != fast){
        slow = nums[slow];
        fast = nums[fast];
    }

    return slow;  
}

FibOfN.java

class Solution {
    public int fib(int n) {

        if(n <= 1){
            return n;
        }

        int prev = 0;
        int current = 1;

        for(int i=2; i<=n; i++){
            int next = prev + current;
            prev = current;
            current = next;
        }

        return current;
    }
}

IndeciesOfTheTargetSumProblem.java

import java.util.HashMap;

class IndeciesOfTheTargetSumProblem {
    
    public static int[] indeciesOfTarget(int target, int[] array){
        int[] indecies = new int[2];
        HashMap<Integer, Integer> numberNIndecies = new HashMap<>();
        
        for(int i=0; i< array.length; i++){
            int difference = target - array[i];
            if (numberNIndecies.containsKey(difference)) {
                indecies[0] = numberNIndecies.get(difference);
                indecies[1] = i;
                return indecies;
            }
            numberNIndecies.put(array[i], i);
        }
        
        return indecies;
    }
    
    public static void main(String[] args) {
        int[] arr = {1, 2, 3, 4, 5};
        int[] arr2 = indeciesOfTarget(4, arr);
        
        System.out.println(arr2[0] + " " + arr2[1]);
    }
}

MaxProfitFromTheStockPrices.java

class MaxProfitFromTheStockPrices {
    
    public static int maxProfit(int[] arr) {
        int buyPointer = 0;
        int sellPointer = 1;
        int maxProfit = 0;
        
        while(sellPointer < arr.length){
            if(arr[buyPointer] < arr[sellPointer]){
                int profit = arr[sellPointer] - arr[buyPointer];
                if(profit > maxProfit){
                    maxProfit = profit;
                }
            }else{
                buyPointer = sellPointer;
            }
            
            sellPointer ++;
        }
        
        return maxProfit;
    }
    
    public static void main(String[] args) {
        int[] arr = {7, 1, 5, 3, 6, 7, 4};
    
        System.out.println(maxProfit(arr));
    }
}

MissingNumberInSeries.java

class Solution {
    public int missingNumber(int[] nums) {

        int arraySum =0;
        int size = nums.length;
        int formullaSum = (size * (size + 1))/2;

        for(int num : nums){
            arraySum += num;
        }

        return (formullaSum - arraySum);

    }
}

ReverseALinkList.java

public ListNode reverseList(ListNode head) {
    ListNode prev = null;
    ListNode current = head;
    ListNode next = null;

    while(current != null){
        next = current.next;
        current.next = prev;
        prev = current;
        current = next;
    }

    return prev;
}