Created potd_22_10_2024.java

october_2024/potd_22_10_2024.java

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+/*
+Problem:
+Given an array arr[] and two integers say, x and y, find the number of sub-arrays in which the number of occurrences of x is equal to the number of occurrences of y.
+
+Example:
+Input: arr[] = [1, 2, 1] , x= 1 , y = 2
+Output: 2
+Explanation: The possible sub-arrays have same equal number of occurrences of x and y are:
+1) [1, 2], x and y have same occurrence(1).
+2) [2, 1], x and y have same occurrence(1).
+
+*/
+
+import java.util.HashMap;
+
+public class EqualOccurrences {
+    public static int countEqualOccurrences(int[] arr, int x, int y) {
+        // HashMap to store the frequency of count differences.
+        HashMap<Integer, Integer> countMap = new HashMap<>();
+        int countDiff = 0;  // Tracks the difference between counts of x and y.
+        int result = 0;     // Stores the number of valid subarrays.
+
+        // Initialize the map with countDiff 0 (initial state).
+        countMap.put(0, 1);
+
+        // Traverse the array and update the count difference.
+        for (int num : arr) {
+            if (num == x) {
+                countDiff++;  // Increment if the element is x.
+            } else if (num == y) {
+                countDiff--;  // Decrement if the element is y.
+            }
+
+            // If this countDiff was seen before, it means there's a valid subarray.
+            result += countMap.getOrDefault(countDiff, 0);
+
+            // Update the frequency of the current countDiff in the map.
+            countMap.put(countDiff, countMap.getOrDefault(countDiff, 0) + 1);
+        }
+
+        return result;
+    }
+
+    public static void main(String[] args) {
+        int[] arr = {1, 2, 1};
+        int x = 1, y = 2;
+
+        int result = countEqualOccurrences(arr, x, y);
+        System.out.println("Number of subarrays with equal occurrences of " + x + " and " + y + ": " + result);
+    }
+}