#N1512. Number of Good Pairs
problem link=>https://leetcode.com/problems/number-of-good-pairs/

#solution

class Solution {
    public int numIdenticalPairs(int[] nums) {
        int good=0;
        for(int i=0; i<nums.length-1; i++){
            for(int j=i+1; j<nums.length; j++){
                if(nums[i]==nums[j])
                    good++;
            }
        }
        
        return good;
    }
}

#N1365. How Many Numbers Are Smaller Than the Current Number
problem link=>https://leetcode.com/problems/how-many-numbers-are-smaller-than-the-current-number/

#solution

class Solution {
    public int[] smallerNumbersThanCurrent(int[] nums) {
        int[] ans=new int[nums.length];
        int count=0;
        for(int i=0; i<nums.length; i++){
            for(int j=0; j<nums.length; j++){
                if(nums[i]>nums[j]&&j!=i){
                    count++;
                }
            }
            ans[i]=count;
            count=0;
        }
        return ans;
    }
}

#medium

#N1395. Count Number of Teams
problem link=>https://leetcode.com/problems/count-number-of-teams/

#solution

class Solution {
    public int numTeams(int[] rating) {
        int res = 0;
        
        for (int i = 1; i < rating.length - 1; ++i) {
            
            int less[] = new int[2], greater[] = new int[2];
            
            for (int j = 0; j < rating.length; ++j) {
                
                if (rating[i] < rating[j])
                    ++less[j > i ? 1 : 0];
                
                if (rating[i] > rating[j])
                    ++greater[j > i ? 1 : 0];
            }
            
            res += less[0] * greater[1] + greater[0] * less[1];
        }
        
        return res;
    }
}

#N1961. Check If String Is a Prefix of Array
problem link=>https://leetcode.com/problems/check-if-string-is-a-prefix-of-array/

#solution

class Solution {
    public boolean isPrefixString(String s, String[] words) {
        String allWords="";
        
        for(int i=0; i<words.length; i++){
            allWords+=words[i];
            if(allWords.equals(s))
                return true;
        }
        return false;
    }
}

#N1389. Create Target Array in the Given Order
problem link=>https://leetcode.com/problems/create-target-array-in-the-given-order/

#solution

class Solution {
    public int[] createTargetArray(int[] nums, int[] index) {
        int[] target = new int[nums.length];
        int i = 0, k = 0;
        
        while (i < index.length) {
            
            for (k = target.length - 1; k > index[i]; k--)
                target[k] = target[k - 1];
            
            target[index[i]] = nums[i];
            i++;
        }
        
        return target;
    }
}

‼️P.s. Without ArrayLists. It would be simple and no-logic with ArrayLists

#N1528. Shuffle String
problem link=>https://leetcode.com/problems/shuffle-string/

#solution

class Solution {
    public String restoreString(String s, int[] indices) {
        char[] ch=new char[s.length()];
        for (int i = 0; i < s.length(); i++) {
            ch[i] = s.charAt(i);
        }
        char[] newch=new char[ch.length];
        for(int i=0; i<indices.length;i++){
            newch[indices[i]]=ch[i];
        }
        
        
        return new String(newch);
    }
}

#N1720. Decode XORed Array
problem link=>https://leetcode.com/problems/decode-xored-array/

#solution

class Solution {
    public int[] decode(int[] encoded, int first) {
        int[] arr=new int[encoded.length+1];
        arr[0]=first;
        for(int i=0; i<encoded.length; i++){
            arr[i+1]=arr[i]^encoded[i];
        }
        
        return arr;
    }
}

#N961. N-Repeated Element in Size 2N Array
problem link=>https://leetcode.com/problems/n-repeated-element-in-size-2n-array/

#solution

class Solution {
    public int repeatedNTimes(int[] nums) {
        int arr[]=new int[10000];
        for(int i=0; i<nums.length; i++){
            if(++arr[nums[i]]==2)
                return nums[i];
        }
        return 0;
    }
}

#N942. DI String Match
problem link=>https://leetcode.com/problems/di-string-match/

#solution

class Solution {
    public int[] diStringMatch(String s) {
        char[] ch=s.toCharArray();
        int[] arr=new int[ch.length+1];
        int I0=0, Dn=ch.length;
        for(int i=0; i<ch.length; i++){
            if(ch[i]=='I')
                arr[i]=I0++;
            if(ch[i]=='D')
                arr[i]=Dn--;
        }
        
        arr[arr.length-1]=I0;
        
        return arr;
    }
}

#N1748. Sum of Unique Elements
problem link=>https://leetcode.com/problems/sum-of-unique-elements/

#solution

class Solution {
    public int sumOfUnique(int[] nums) {
        int countFrequency[]=new int[101];
        for(int num:nums){
            ++countFrequency[num];
        }
        
        int sum=0;
        
        for(int i=0; i<countFrequency.length; i++){
            if(countFrequency[i]==1)
                sum+=i;
        }
        
        return sum;
    }
}

#N9. Palindrome Number
problem link=>https://leetcode.com/problems/palindrome-number/

#solution

class Solution {
    public boolean isPalindrome(int x) {
        if(x<0) return false;
        int num=x;
        int palindrome=0;
        int temp=0;
        while(true){
            temp=x%10;
            x/=10;
            palindrome=palindrome*10+temp;
            if(x==0)
                break;
        }
        
        return num==palindrome;
    }
}

#N13. Roman to Integer
problem link=>https://leetcode.com/problems/roman-to-integer/

#solution

class Solution {
    public int romanToInt(String s) {
        int nums[]=new int[s.length()];
        int temp=0;
        int num=0;
        
        for(int i=0; i<s.length(); i++){
            if(s.charAt(i)=='I') nums[i]=1;
            if(s.charAt(i)=='V') nums[i]=5;
            if(s.charAt(i)=='X') nums[i]=10;
            if(s.charAt(i)=='L') nums[i]=50;
            if(s.charAt(i)=='C') nums[i]=100;
            if(s.charAt(i)=='D') nums[i]=500;
            if(s.charAt(i)=='M') nums[i]=1000;
        }
        
        for(int i=0; i<nums.length-1; i++){
            if(nums[i]<nums[i+1]){
                num-=nums[i];
            }else
                num+=nums[i];
        }
        num+=nums[nums.length-1];
        return num;
    }
}

#N67. Add Binary
problem link=>https://leetcode.com/problems/add-binary/

#solution

class Solution {
    public String addBinary(String a, String b) {
        int lena = a.length();
        int lenb = b.length();
        int i =0, qarz = 0;
        String res = "";
        while(i<lena || i<lenb || qarz!=0){
            int x = (i<lena) ? Integer.parseInt(""+a.charAt(lena - 1 - i)) : 0;
            int y = (i<lenb) ? Integer.parseInt(""+b.charAt(lenb - 1 - i)) : 0;
            res = (x + y + qarz)%2 + res;
            qarz = (x + y + qarz)/2;
            i++;
        }
        
        return res;
    }
}

#N69. Sqrt(x)
problem link=>https://leetcode.com/problems/sqrtx/

#solution

class Solution {
    public int mySqrt(int x) {
        if (x == 0) return 0;
     int start = 1, end = x;
     while (start < end) { 
  int mid = (start + end) / 2;
  if (mid <= x / mid && (mid + 1) > x / (mid + 1))
   return mid; 
  else if (mid > x / mid)
   end = mid;
  else
   start = mid + 1;
     }
     return start;
    }
}

#N70. Climbing Stairs
problem link=>https://leetcode.com/problems/climbing-stairs/

#solution

class Solution {
    public int climbStairs(int n) {
        int fib=0, x=1, y=1;         
        for(int i=1; i<n; i++){
            fib=y;
            y=x+y;
            x=fib;
        }
        
        return y;
    }
}

#N2037. Minimum Number of Moves to Seat Everyone
problem link=>https://leetcode.com/problems/minimum-number-of-moves-to-seat-everyone/

#solution

class Solution {
    public int minMovesToSeat(int[] seats, int[] students) {
        Arrays.sort(seats);
        Arrays.sort(students);
        int balance=0;
        for(int i=0; i<seats.length; i++){
            balance+=Math.abs(students[i]-seats[i]);
        }
        
        return balance;
    }
}

#N905. Sort Array By Parity
problem link=>https://leetcode.com/problems/sort-array-by-parity/

#solution

class Solution {
    public int[] sortArrayByParity(int[] nums) {
        int temp=0;
        for(int i=0; i<nums.length-1; i++){
            for(int j=0; j<nums.length-i-1; j++){
                if(nums[j]%2==1&&nums[j+1]%2==0){
                    temp=nums[j];
                    nums[j]=nums[j+1];
                    nums[j+1]=temp;
                }
            }
        }
        
        return nums;
    }
}

#N561. Array Partition I
problem link=>https://leetcode.com/problems/array-partition-i/

#solution

class Solution {
    public int arrayPairSum(int[] nums) {
        Arrays.sort(nums);
        int sum=0;
        for(int i=0; i<nums.length; i=i+2){
            sum+=nums[i];
        }
        
        return sum;
    }
}

#N704. Binary Search
problem link=>https://leetcode.com/problems/binary-search/

#solution

class Solution {
    public int search(int[] nums, int target) {
        int left=0, right=nums.length-1, mid;
        while(left<=right){
            mid=(left+right)/2;
            if(nums[mid]<target){
                left=mid+1;
            }
            if(nums[mid]>target){
                right=mid-1;
            }
            
            if(nums[mid]==target){
                return mid;
            }
        }
        
        return -1;
    }
}

‼️Implementation of Bineary Search to the problems

#N1346. Check If N and Its Double Exist
problem link=>https://leetcode.com/problems/check-if-n-and-its-double-exist/

#solution

class Solution {
    public boolean checkIfExist(int[] arr) {
        for(int i=0; i<arr.length; i++){
            for(int j=0; j<arr.length; j++){
                if(arr[i]==2*arr[j]&&i!=j)
                    return true;
            }
        }
        
        return false;
    }
}