Problem 1: Palindrome Number

Link to the problem: https://leetcode.com/problems/palindrome-number/

class Solution {
    public boolean isPalindrome(int x) {
        StringBuilder sb = new StringBuilder(Integer.toString(x));
        System.out.println(sb+" "+sb.reverse());
        return sb.toString().equals(sb.reverse().toString())?true:false;
    }
}

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Problem 2: Reverse Bits

Link to the problem: https://leetcode.com/problems/reverse-bits/

public class Solution {
    public int reverseBits(int n) {
        int result = 0;
        for (int i = 0; i < 32; i++) {
            int bit = n & 1;
            result = (result << 1) | bit;
            n = n >>> 1;
        }
        return result;
    }
}

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Problem 3: Maximum Subarray

Link to the problem: leetcode.com/problems/maximum-subarray/

class Solution {
    public int maxSubArray(int[] nums) {
        int sum = 0;
        int maxSum = nums[0];

        for(int num : nums){
            sum += num;
            maxSum = sum > maxSum ? sum : maxSum;
            if(sum < 0){
                sum = 0;
            }
        }
        return maxSum;
    }
}

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Problem 4: Find the original String II

Link to the problem: https://leetcode.com/problems/find-the-original-typed-string-ii/

public class Solution {
    private static final int MOD = (int)1e9 + 7;

    public int possibleStringCount(String word, int k) {
        if (word.isEmpty()) return 0;

        List<Integer> groups = new ArrayList<>();
        int count = 1;
        for (int i = 1; i < word.length(); i++) {
            if (word.charAt(i) == word.charAt(i - 1)) count++;
            else {
                groups.add(count);
                count = 1;
            }
        }
        groups.add(count);

        long total = 1;
        for (int num : groups) total = (total * num) % MOD;

        if (k <= groups.size()) return (int)total;

        int[] dp = new int[k];
        dp[0] = 1;
        for (int num : groups) {
            int[] newDp = new int[k];
            long sum = 0;
            for (int s = 0; s < k; s++) {
                if (s > 0) sum = (sum + dp[s - 1]) % MOD;
                if (s > num) sum = (sum - dp[s - num - 1] + MOD) % MOD;
                newDp[s] = (int)sum;
            }
            dp = newDp;
        }
        long invalid = 0;
        for (int s = groups.size(); s < k; s++) invalid = (invalid + dp[s]) % MOD;

        return (int)((total - invalid + MOD) % MOD);
    }
}

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Problem 5: Insert Interval

Link to the problem: https://leetcode.com/problems/insert-interval/

class Solution {
    public int[][] insert(int[][] intervals, int[] newInterval) {

        List<int[]> res = new ArrayList<>();

        for (int i = 0; i < intervals.length; i++) {
            if(intervals[i][0] > newInterval[1]) {
                res.add(newInterval);
                while(i < intervals.length)
                    res.add(intervals[i++]);
                return res.toArray(new int[res.size()][]);
            }else if(intervals[i][1] < newInterval[0]) {
                res.add(intervals[i]);
            }else{
                newInterval[0] = Math.min(newInterval[0], intervals[i][0]);
                newInterval[1] = Math.max(newInterval[1], intervals[i][1]);
            }
        }

        res.add(newInterval);
        return res.toArray(new int[res.size()][]);
    }
}

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