#N888. Fair Candy Swap
problem link

#solution

class Solution {
    public int[] fairCandySwap(int[] a, int[] b) {
        int sumA = 0, sumB = 0;
        for(int n: a) sumA+=n;
        for(int n: b) sumB+=n;
        
        int delta = (sumB - sumA) / 2;
        
        Set<Integer> set = new HashSet<>();
        for(int n: b) set.add(n);
        
        for(int n: a)
            if(set.contains(n+delta)) return new int[]{n, n+delta};
        
        return new int[0];
    }
}

#N283. Move Zeroes
problem link

#solution

class Solution {
    public void moveZeroes(int[] nums) {
        int index = 0;
        
        for (int n: nums)
            if(n != 0)
                nums[index++] = n;
        
        while(index<nums.length)
            nums[index++] = 0;
        
    }
}

#N1848. Minimum Distance to the Target Element
problem link

#solution

class Solution {
    public int getMinDistance(int[] nums, int target, int start) {
        int ans = Integer.MAX_VALUE;
        
        for(int i=0; i<nums.length; i++){
            if(nums[i] == target)
                ans = Math.min(ans, Math.abs(i - start));
        }
        
        return ans;
    }
}

#N1287. Element Appearing More Than 25% In Sorted Array
problem link

#solution

class Solution {
    public int findSpecialInteger(int[] arr) {
        int length = arr.length, quart = length/4;
        
        for(int i=0; i<length - quart; i++)
            if(arr[i] == arr[i+quart]) return arr[i];
        
        return -1;
    }
}

#N748. Shortest Completing Word
problem link

#solution

Map<Character, Integer> map=new HashMap<>();
        int minLength=Integer.MAX_VALUE;
        String result = null;
        for(char ch: licensePlate.toLowerCase().toCharArray())
            if(Character.isLetter(ch))map.put(ch, map.getOrDefault(ch, 0) +1);
        for(String word:words){
            System.out.println(word);
            Map<Character, Integer> temp = new HashMap<>(map);
            int count = temp.size();
            for(char ch:word.toCharArray())
                if(temp.containsKey(ch))temp.put(ch, temp.get(ch) -1);
            
            for(Map.Entry<Character, Integer> entry: temp.entrySet()){
                if(entry.getValue()>0) break;
                count--;
            }
            if(count<=0&&minLength>word.length()){
                result=word;
                minLength=word.length();
            }
        }
        return result;

#N1629. Slowest Key
problem link

#solution

class Solution {
    public char slowestKey(int[] releaseTimes, String str) {
        int max=releaseTimes[0], ix=0;
        
        for(int i=1; i<releaseTimes.length; i++){
            if(max<=releaseTimes[i]-releaseTimes[i-1]){
                if(max==releaseTimes[i]-releaseTimes[i-1]&&str.charAt(i)>str.charAt(ix)){
                    ix=i;
                    //break;
                }else if(max<releaseTimes[i]-releaseTimes[i-1]){
                max=releaseTimes[i]-releaseTimes[i-1];
                ix=i;}
            }
        }
        
        return str.charAt(ix);
    }
}

#N217. Contains Duplicate
problem link

#solution

class Solution {
    public boolean containsDuplicate(int[] nums) {
        if(nums == null){
            return false;
        }
        
        int len = nums.length;
        HashSet<Integer> set = new HashSet<Integer>();
        for(int i = 0; i < len; i++){
            if(!set.add(nums[i])){
                return true;
            }
        }
        return false;

    }
}

#N896. Monotonic Array
problem link

#solution

class Solution {
    public boolean isMonotonic(int[] nums) {
        int countI=0, countD=0, l=nums.length;
        for(int i=0; i<l-1; i++){
            if(nums[i] == nums[i+1]){
                countI++;
                countD++;
            }
            else if(nums[i] < nums[i+1]) countI++;
            else countD++;
        }
        
        return countI == l-1 || countD == l-1;
    }
}

#N1331. Rank Transform of an Array
problem link

#solution

class Solution {
    public int[] arrayRankTransform(int[] arr) {
        int[] helper = Arrays.copyOf(arr, arr.length);
        Arrays.sort(helper);
        Map<Integer, Integer> rank = new HashMap<>();
        int pos=1;
        for(int n: helper)
            if(rank.getOrDefault(n, 0) == 0) rank.put(n, rank.size()+1);
        
        for(int i=0; i<arr.length; i++)
            arr[i] = rank.get(arr[i]);
        
        return arr;
    }
}

#N1560. Most Visited Sector in a Circular Track
problem link

#solution

class Solution {
    public List<Integer> mostVisited(int n, int[] rounds) {
        int l=rounds.length;
        List<Integer> list = new ArrayList<>();
        
        for(int i=rounds[0]; i<=rounds[l-1]; i++)
            list.add(i);
        
        if(list.size()>0) return list;
        
        for(int i=1; i<=rounds[l-1]; i++)
            list.add(i);
        for(int i=rounds[0]; i<=n; i++)
            list.add(i);
        
        return list;
    }
}

#N167. Two Sum II - Input Array Is Sorted
problem link

#solution

class Solution {
    public int[] twoSum(int[] numbers, int target) {
        int start = 0, end = numbers.length - 1;
        while(start < end){
            if(numbers[start] + numbers[end] == target) break;
            if(numbers[start] + numbers[end] < target) start++;
            else end--;
        }
        return new int[]{start + 1, end + 1};
    }
}

#N1370. Increasing Decreasing String
problem link

#solution

class Solution {
    public String sortString(String s) {
        int count[] = new int[26];
        StringBuilder sb=new StringBuilder();
        for(char ch: s.toCharArray())
            count[ch-'a']++;
        
        while(sb.toString().length()<s.length()){
            for(int i=0; i<26; i++){
                if(count[i]>0){
                    sb.append((char) (i+'a'));
                    count[i]--;
                }
            }
            
            for(int i=25; i>=0; i--){
                if(count[i]>0){
                    sb.append((char) (i+'a'));
                    count[i]--;
                }
            }
        }
        
        return sb.toString();
    }
}

#N1436. Destination City
problem link

#solution

class Solution {
    public String destCity(List<List<String>> paths) {
        Map<String, Integer> map = new HashMap<>();
        
        for(List<String> list: paths){
            map.put(list.get(0), map.getOrDefault(list.get(0), 0) -1);
            map.put(list.get(1), map.getOrDefault(list.get(1), 0) +1);
        }
        
        for(Map.Entry<String, Integer> entry: map.entrySet())
            if(entry.getValue()>0) return entry.getKey();
        
        return new String();
    }
}

#N1374. Generate a String With Characters That Have Odd Counts
problem link

#solution

class Solution {
    public String generateTheString(int n) {
        StringBuilder sb = new StringBuilder();
        
        for(int i=0; i<n-1; i++)
            sb.append('a');
        
        return (n%2==0)?sb.append('b').toString():sb.append('a').toString();
    }
}

#statistics
Till this time, 192 in total,
180 easy;
12 medium;
type of problem solutions have been posted

#N1941. Check if All Characters Have Equal Number of Occurrences
problem link

#solution

class Solution {
    public boolean areOccurrencesEqual(String s) {
        int freq[] = new int[26], count=0;
        char temp=s.charAt(0);
        
        for(char ch: s.toCharArray()){
            if(ch == temp) count++;
            freq[ch-'a']++;
        }
        
        for(int i: freq)
            if(i != 0 && i != count) return false;
        
        return true;
    }
}

#N557. Reverse Words in a String III
problem link

#solution

class Solution {
    public String reverseWords(String s) {
        StringBuilder sb = new StringBuilder();
        String[] words = s.split(" ");
        
        for(String word: words){
            sb.append(" ");
            
            sb.append(new StringBuilder(word).reverse());
        }
        
        return sb.toString().trim();
    }
}

#N657. Robot Return to Origin
problem link

#solution

class Solution {
    public boolean judgeCircle(String moves) {
        int[] count = new int[4];
        
        for(char ch: moves.toCharArray()){
            if(ch == 'R') count[0]++;
            else if(ch == 'L') count[1]++;
            else if(ch == 'U') count[2]++;
            else count[3]++;
        }
        
        return count[0] - count[1] == 0 && count[2] - count[3] == 0;
    }
}

#N1768. Merge Strings Alternately
problem link

#solution

class Solution {
    public String mergeAlternately(String word1, String word2) {
        StringBuilder sb = new StringBuilder();
        
        for(int i = 0; i<Math.max(word1.length(), word2.length()); i++){
            if(word1.length()>i)
                sb.append(word1.charAt(i));
            
            if(word2.length()>i)
                sb.append(word2.charAt(i));

        }
        
        return sb.toString();
    }
}

#N344. Reverse String
problem link

#solution

class Solution {
    public void reverseString(char[] s) {
        for(int i=0; i<s.length/2; i++){ 
            char tmp = s[i];
            s[i] = s[s.length-1-i];
            s[s.length-1-i] = tmp; 
        }
    }
}