Add the solution for LC #2537

Author: rayworks

src/main/java/org/sean/array/GoodSubarrayCounter.java

@@ -0,0 +1,63 @@
+package org.sean.array;
+
+import java.util.HashMap;
+
+/***
+ * 2537. Count the Number of Good Subarrays
+ */
+public class GoodSubarrayCounter {
+    public long countGood(int[] nums, int k) {
+        int len = nums.length;
+        int left = 0, right = 0;
+
+        int currPairCnt = 0;
+        long res = 0L;
+        HashMap<Integer, Integer> map = new HashMap<>();
+
+        while (left < len && right < len) {
+            while (right < len) {
+                int elem = nums[right];
+
+                if (map.containsKey(elem)) {
+                    int cnt = map.get(elem);
+                    currPairCnt += cnt;
+                    map.put(elem, cnt + 1);
+                } else {
+                    map.put(elem, 1);
+                }
+                if (currPairCnt >= k) {
+                    int add = len - right;
+                    res += add;
+                    // System.out.printf("%d matched substring found, range from %d to %d\n", add, left, right);
+                    break;
+                }
+
+                right++;
+            }
+
+            while (currPairCnt >= k && left < right) {
+                int leftElem = nums[left];
+                int leftCnt = map.getOrDefault(leftElem, 0);
+
+                // relax from left side
+                map.put(leftElem, leftCnt - 1);
+                if (leftCnt == 1)
+                    map.remove(leftElem);
+
+                currPairCnt -= leftCnt - 1; // the num of increased pairs
+                left++;
+
+                if (currPairCnt >= k) {
+                    // System.out.printf("matched substring found, range from %d to %d\n", left, right);
+                    // [left', right...]
+                    res += len - right;
+                }
+            }
+
+            // advance the right pointer
+            right++;
+        }
+
+        return res;
+    }
+}

src/test/java/org/sean/array/GoodSubarrayCounterTest.java

@@ -0,0 +1,22 @@
+package org.sean.array;
+
+import org.junit.Before;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class GoodSubarrayCounterTest {
+
+    private GoodSubarrayCounter counter;
+
+    @Before
+    public void setUp() throws Exception {
+        counter = new GoodSubarrayCounter();
+    }
+
+    @Test
+    public void countGood() {
+        long ans = counter.countGood(new int[]{3, 1, 4, 3, 2, 2, 4, 3, 1, 4, 3, 2}, 2);
+        assertEquals(31, ans);
+    }
+}