LeetCode Weekly Contest 484 Discussion and Solution

Problem-by-Problem Breakdown

Problem 1 - Count Residue Prefixes

Approach

class Solution {
    public int residuePrefixes(String s) {
        int n = s.length();

        Set<Character> set = new HashSet<>();
        int ans = 0;

        for(int i = 0; i < n; i++){
            char ch = s.charAt(i);
            set.add(ch);

            if((i + 1) % 3 == set.size()) ans++;
        }

        return ans;
    }
}

Problem 2 - Number of Centered Subarrays

Approach

class Solution {
    public int centeredSubarrays(int[] nums) {
        int n = nums.length;
        int ans = 0;
        
        for(int i = 0; i < n; i++){
            Set<Integer> set = new HashSet<>();
            int sum = 0;

            for(int j = i; j < n; j++){
                sum += nums[j];
                set.add(nums[j]);

                if(set.contains(sum)) ans++;
            }
        }

        return ans;
    }
}

Problem 3 - Count Caesar Cipher Pairs

• Choose either s or t.
• Replace every letter in the chosen string with the next letter in the alphabet cyclically. The next letter after 'z' is 'a'.

• i < j
• words[i] and words[j] are similar.

Approach

class Solution {
    public long countPairs(String[] words) {
        
        Map<String, Integer> map = new HashMap<>();
        long ans = 0;

        for(String word : words){

            StringBuilder sb = new StringBuilder();
            int baseVal = (int) word.charAt(0);

            for(int i = 0; i < word.length(); i++){

                int currVal = (int) word.charAt(i);
                int relativeVal = (currVal - baseVal + 26) % 26;

                sb.append(Integer.toString(relativeVal));
            }

            String s = sb.toString();

            if(map.containsKey(s)) ans += map.get(s);
            map.put(s, map.getOrDefault(s, 0) + 1);
        }

        return ans;
    }
}

Problem 4 - Maximum Bitwise AND After Increment Operations

Approach

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