Problem 1: Majority Element

Link to the problem: https://leetcode.com/problems/majority-element/

class Solution {
    public int majorityElement(int[] nums) {
        HashMap<Integer, Integer> map = new HashMap<>();
        for(int i:nums){
            if(map.containsKey(i))
                map.put(i, map.get(i)+1);
            else
                map.put(i, 1);
        }
        int max = 0;
        int ans = 0;
        for(Map.Entry e:map.entrySet()){
            if(max<(int) e.getValue()){
                max = (int) e.getValue();
                ans = (int) e.getKey();
            }
        }
        return ans;
    }
}

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Problem 2: Valid Anagram

Link to the problem: https://leetcode.com/problems/valid-anagram/

class Solution {
    public boolean isAnagram(String s, String t) {
        if(s.length()!=t.length())
            return false;
        HashMap<Character, Integer> map1 = new HashMap<>();
        HashMap<Character, Integer> map2 = new HashMap<>();
        for(int i=0; i<s.length(); i++){
            char char1 = s.charAt(i);
            char char2 = t.charAt(i);
            if(map1.containsKey(char1))
                map1.put(char1, map1.get(char1)+1);
            else
                map1.put(char1, 1);
            if(map2.containsKey(char2))
                map2.put(char2, map2.get(char2)+1);
            else
                map2.put(char2, 1);
        }
        if(!map1.equals(map2))
            return false;
        return true;
    }
}

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Problem 3: Max Consecutive Ones

Link to the problem: https://leetcode.com/problems/max-consecutive-ones/

class Solution {
    public int findMaxConsecutiveOnes(int[] nums) {
        int count = 0;
        int ans = 0;
        for(int i:nums){
            if(i==1)
                count++;
            else{
                ans = ans>count?ans:count;
                count=0;
            }
        }
        return ans>count?ans:count;
    }
}

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Problem 4: Next Greater Element I

Link to the problem: https://leetcode.com/problems/next-greater-element-i/

class Solution {
    public int[] nextGreaterElement(int[] nums1, int[] nums2) {
        int[] ans = new int[nums1.length];
        for(int i=0; i<nums1.length; i++){
            int j=0;
            while(nums2[j]!=nums1[i])
                j++;
            int index = j;
            j++;
            while(j<nums2.length && nums2[j]<nums2[index])
                j++;
            if(j>nums2.length-1)
                ans[i]=-1;
            else 
                ans[i]=nums2[j];
        }
        return ans;
    }
}

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Problem 5: Set Mismatch

Link to the problem: https://leetcode.com/problems/set-mismatch/

class Solution {
    public int[] findErrorNums(int[] nums) {
        HashMap<Integer, Integer> map = new HashMap<>();
        int[] ans = new int[2];
        for(int i:nums){
            if(map.containsKey(i))
                ans[0] = i;
            else
                map.put(i, 1);
        }
        for(int i=1; i<=nums.length; i++){
            if(!map.containsKey(i)){
                ans[1] = i;
                break;
            }
        }
        return ans;
    }
}

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