Problem 1: Kth Largest Element in an Array

Link to the problem: https://leetcode.com/problems/kth-largest-element-in-an-array/

class Solution {
    public int findKthLargest(int[] nums, int k) {
        PriorityQueue<Integer> pq = new PriorityQueue<>();
        for(int i:nums) pq.offer(i);
        while(pq.size()>k) pq.poll();
        return ((Integer) pq.peek()).intValue();
    }
}

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Problem 2: Longest Mountain in Array

Link to the problem: https://leetcode.com/problems/longest-mountain-in-array/

class Solution {
    public int longestMountain(int[] arr) {
        int n = arr.length;
        if(n<3) return 0;

        int i=1;
        int res = 0;

        while(i<n-1){
            boolean isPeak = ((arr[i]>arr[i-1]) && arr[i]>arr[i+1]);
            if(isPeak){
                int left = i;
                int right = i;
                while(left>0 && arr[left]>arr[left-1]) left--;
                while(right<n-1 && arr[right]>arr[right+1]) right++;
                int currLen = right-left+1;
                res = Math.max(res, currLen);
                i=right;
            }else{
                i++;
            }
        }

        return res;
    }
}

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Problem 3: Majority Element

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

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

        int count = 0;
        int candidate = -1;

        for(int i:nums){
            if(count==0){
                count++;
                candidate = i;
            }else if(candidate==i) count++;
            else{
                count--;
                if(count==0){
                    count++;
                    candidate = i;
                }
            }
        }

        count = 0;
        for(int i:nums) if(candidate==i) count++;

        return count>nums.length/2?candidate:-1;
    }
}

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Problem 4: Sliding Window Maximum

Link to the problem: https://leetcode.com/problems/sliding-window-maximum/

class Solution {
    public int[] maxSlidingWindow(int[] nums, int k) {
        int n = nums.length;

        if(k>=n){
            int num = Integer.MIN_VALUE;
            for(int i:nums) num = Math.max(num, i);
            int[] res = new int[1];
            res[0] = num;
            return res;
        }

        ArrayList<Integer> list = new ArrayList<>();
        Deque<Integer> dq = new ArrayDeque<>();

        for(int i=0; i<k; i++){
            while(!dq.isEmpty() && nums[dq.peekLast()]<=nums[i]) dq.pollLast();
            dq.addLast(i);
        }

        for(int i=k; i<n; i++){
            list.add(nums[dq.peekFirst()]);
            while(!dq.isEmpty() && dq.peekFirst()<i-k+1) dq.pollFirst();
            while(!dq.isEmpty() && nums[dq.peekLast()]<=nums[i]) dq.pollLast();
            dq.addLast(i);
        }

        list.add(nums[dq.peekFirst()]);

        int[] res = new int[list.size()];
        for(int i=0; i<list.size(); i++) res[i] = ((Integer) list.get(i)).intValue();

        return res;
    }
}

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Problem 5: Last Moment before all Ants Fall Of a Plank

Link to the problem: https://leetcode.com/problems/last-moment-before-all-ants-fall-out-of-a-plank/

class Solution {
    public int getLastMoment(int n, int[] left, int[] right) {
        int res = 0;
        for(int i:left) res = Math.max(res, i);
        for(int i:right) res = Math.max(res, n-i);
        return res;
    }
}

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