Longest subarray sum equals K

Author: nlohia-godaddy

src/main/java/leetcode/medium/LongestSubarraySumEqualsK.java

@@ -0,0 +1,29 @@
+package leetcode.medium;
+
+import java.util.HashMap;
+import java.util.Map;
+
+public class LongestSubarraySumEqualsK {
+
+  int longestSubarray(int[] arr, int k) {
+    Map<Integer, Integer> sumSeenIndexMap = new HashMap<>();
+    int res = 0;
+    int prefSum = 0;
+
+    for (int i = 0; i < arr.length; ++i) {
+      prefSum += arr[i];
+
+      // If prefixSum - k exists in the map then there exist such
+      // subarray from (index of previous prefix + 1) to i.
+      if (sumSeenIndexMap.containsKey(prefSum - k))
+        res = Math.max(res, i - sumSeenIndexMap.get(prefSum - k));
+
+      // Store only first occurrence index of prefSum
+      if (!sumSeenIndexMap.containsKey(prefSum))
+        sumSeenIndexMap.put(prefSum, i);
+    }
+
+    return res;
+  }
+
+}

src/test/java/leetcode/medium/LongestSubarraySumEqualsKTest.java

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+package leetcode.medium;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+class LongestSubarraySumEqualsKTest {
+
+  private final LongestSubarraySumEqualsK longestSubarraySumEqualsK;
+
+  LongestSubarraySumEqualsKTest() {
+    longestSubarraySumEqualsK = new LongestSubarraySumEqualsK();
+  }
+
+  @Test
+  void testLongestSubarray1() {
+    int[] nums = {1, -1, 5, -2, 3};
+    int k = 3;
+    assertEquals(2, longestSubarraySumEqualsK.longestSubarray(nums, k));
+  }
+
+  @Test
+  void testLongestSubarray2() {
+    int[] nums = {-2, -1, 2, 1};
+    int k = 1;
+    assertEquals(2, longestSubarraySumEqualsK.longestSubarray(nums, k));
+  }
+
+  @Test
+  void testLongestSubarray3() {
+    int[] nums = {10, 2, 2, 7, 8 , 1, 1, 1, 1, -10};
+    int k = 4;
+    assertEquals(4, longestSubarraySumEqualsK.longestSubarray(nums, k));
+  }
+}