Create 3692-majority-frequency-characters.java

Author: sanajitjana

Easy/3692-majority-frequency-characters.java

@@ -0,0 +1,86 @@
+/**
+ * Link: https://leetcode.com/problems/majority-frequency-characters/
+ * Title: Majority Frequency Characters
+ *
+ * Question:
+ * You are given a string s consisting of lowercase English letters.
+ *
+ * The frequency group for a value k is the set of characters that appear exactly k times in s.
+ * The majority frequency group is the group that contains the largest number of distinct characters.
+ * If two or more groups tie for the largest size, choose the group with the larger frequency k.
+ *
+ * Return a string containing all characters in the majority frequency group, in any order.
+ *
+ * --------------------------------------------------------------------
+ * Approach:
+ * - Step 1: Count frequencies of each character using a HashMap.
+ * - Step 2: Build frequency groups: for each frequency k, store all characters that appear k times.
+ * - Step 3: Iterate over all groups:
+ *      - Track the group with the maximum size (# of distinct characters).
+ *      - If there is a tie in size, pick the group with the larger frequency value.
+ * - Step 4: Return the characters of the chosen group.
+ *
+ * --------------------------------------------------------------------
+ * Dry Run:
+ * s = "aabbccc"
+ *
+ * Frequencies:
+ *   a -> 2
+ *   b -> 2
+ *   c -> 3
+ *
+ * Groups:
+ *   freq=2 → "ab"
+ *   freq=3 → "c"
+ *
+ * Group sizes:
+ *   "ab" → size=2
+ *   "c"  → size=1
+ *
+ * Best = "ab" (since size=2 > size=1)
+ * Output = "ab"
+ *
+ * --------------------------------------------------------------------
+ * Time Complexity: O(n)
+ *   - One pass to count frequencies, one pass to build groups,
+ *     one pass to find the best group.
+ * Space Complexity: O(n)
+ *   - Storing frequency map and groups.
+ */
+
+class Solution {
+    public String majorityFrequencyGroup(String s) {
+        // Step 1: frequency map
+        HashMap<Character, Integer> fre = new HashMap<>();
+        for (char ch : s.toCharArray()) {
+            fre.put(ch, fre.getOrDefault(ch, 0) + 1);
+        }
+
+        // Step 2: group by frequency
+        HashMap<Integer, String> group = new HashMap<>();
+        for (Map.Entry<Character, Integer> pair : fre.entrySet()) {
+            int val = pair.getValue();
+            char ch = pair.getKey();
+            group.put(val, group.getOrDefault(val, "") + ch);
+        }
+
+        // Step 3: choose best group
+        int bestSize = 0;
+        int bestFreq = 0;
+        String ans = "";
+
+        for (Map.Entry<Integer, String> pair : group.entrySet()) {
+            String chars = pair.getValue();
+            int freq = pair.getKey();
+            int size = chars.length();
+
+            if (size > bestSize || (size == bestSize && freq > bestFreq)) {
+                bestSize = size;
+                bestFreq = freq;
+                ans = chars;
+            }
+        }
+
+        return ans;
+    }
+}