Problem 1: Find Lucky Integer in an Array

Link to the problem: https://leetcode.com/problems/find-lucky-integer-in-an-array/

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

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Problem 2: Find the Kth Character in String Game II

Link to the problem: https://leetcode.com/problems/find-the-k-th-character-in-string-game-ii/

class Solution {
    public char kthCharacter(long k, int[] operations) {
        int shift = 0; 
        List<Long> lengths = new ArrayList<>();
        long len = 1;

        for (int op : operations) {
            len *= 2;
            lengths.add(len);
            if (len >= k) break;
        }

        for (int i = lengths.size() - 1; i >= 0; i--) {
            long half = lengths.get(i) / 2;
            int op = operations[i];

            if (k > half) {
                k -= half;
                if (op == 1) shift++;
            }
        }

        return (char) ((('a' - 'a' + shift) % 26) + 'a');
    }
}

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Problem 3: Longest Consecutive Sequence

Link to the problem: https://leetcode.com/problems/longest-consecutive-sequence/

class Solution {
    public int longestConsecutive(int[] nums) {
        Map<Integer, Integer> map = new HashMap<>();
        for(int i:nums)
            map.put(i, 1);
        TreeMap<Integer, Integer> sortedMap = new TreeMap<>(map);
        System.out.println(sortedMap);
        int num = Integer.MIN_VALUE;
        int count = 0;
        int ans = Integer.MIN_VALUE;
        for(Map.Entry e:sortedMap.entrySet()){
            int n = ((Integer) e.getKey()).intValue();
            if(num==Integer.MIN_VALUE){
                num = n;
                count++;
            }else{
                if(n==num+1){
                    num = n;
                    count++;
                }else{
                    num=n;
                    ans = ans>count?ans:count;
                    count=1;
                }
            }
        }
        return ans>count?ans:count;
    }
}

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Problem 4: Rotate Array

Link to the problem: https://leetcode.com/problems/rotate-array/

class Solution {
    public void rotate(int[] nums, int k) {
        k=k%nums.length;
        if(nums.length<2)
            return;
        reverseArray(nums, 0, nums.length-k-1);
        reverseArray(nums, nums.length-k, nums.length-1);
        reverseArray(nums, 0, nums.length-1);
    }
    private void reverseArray(int[] nums, int start, int last){
        while(start<last){
            int temp = nums[start];
            nums[start++] = nums[last];
            nums[last--] = temp;
        }
    }
}

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Problem 5: Gas Station

Link to the problem: https://leetcode.com/problems/gas-station/

class Solution {
    public int canCompleteCircuit(int[] gas, int[] cost) {
        for(int i=0; i<gas.length; i++){
            int tank = gas[i];
            if(gas[i]<cost[i] || gas[i]<=1)
                continue;
            int j = (i==gas.length-1)?0:i+1;
            boolean hasGas = true;
            while(j!=i && hasGas){
                int costIndex = (j==0)?gas.length-1:j-1;
                if(tank-cost[costIndex]<0)
                    hasGas=false;
                else{                    
                    tank -= cost[costIndex];
                    tank += gas[j++];
                }
                if(j==gas.length)
                    j=0;
            }
            if(!hasGas)
                continue;
            int index = i==0?gas.length-1:i-1;
            if(tank>=cost[index])
                return i;
        }
        return -1;
    }
}

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