Another solution to "Find the Prefix Common Array of Two Arrays" problem

dkoval · Jan 14, 2025 · 26fe2fe · 26fe2fe
1 parent da581c2
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diff --git a/src/main/java/com/github/dkoval/leetcode/challenge/FindPrefixCommonArrayOfTwoArrays.java b/src/main/java/com/github/dkoval/leetcode/challenge/FindPrefixCommonArrayOfTwoArrays.java
@@ -58,4 +58,29 @@ public int[] findThePrefixCommonArray(int[] A, int[] B) {
             return ans;
         }
     }
+
+    // O(N) time | O(N) space
+    class FindPrefixCommonArrayOfTwoArraysRev2 implements FindPrefixCommonArrayOfTwoArrays {
+
+        @Override
+        public int[] findThePrefixCommonArray(int[] A, int[] B) {
+            final var n = A.length;
+
+            final var ans = new int[n];
+            // 1 <= A[i], B[i] <= n
+            final var counts = new int[n + 1];
+            for (var i = 0; i < n; i++) {
+                if (++counts[A[i]] == 2) {
+                    ans[i]++;
+                }
+
+                if (++counts[B[i]] == 2) {
+                    ans[i]++;
+                }
+
+                ans[i] += (i > 0) ? ans[i - 1] : 0;
+            }
+            return ans;
+        }
+    }
 }
diff --git a/src/test/kotlin/com/github/dkoval/leetcode/challenge/FindPrefixCommonArrayOfTwoArraysTest.kt b/src/test/kotlin/com/github/dkoval/leetcode/challenge/FindPrefixCommonArrayOfTwoArraysTest.kt
@@ -1,6 +1,7 @@
 package com.github.dkoval.leetcode.challenge
 
 import com.github.dkoval.leetcode.challenge.FindPrefixCommonArrayOfTwoArrays.FindPrefixCommonArrayOfTwoArraysRev1
+import com.github.dkoval.leetcode.challenge.FindPrefixCommonArrayOfTwoArrays.FindPrefixCommonArrayOfTwoArraysRev2
 import org.junit.jupiter.api.Assertions.assertArrayEquals
 import org.junit.jupiter.api.Nested
 import org.junit.jupiter.api.extension.ExtensionContext
@@ -37,6 +38,16 @@ internal class FindPrefixCommonArrayOfTwoArraysTest {
             FindPrefixCommonArrayOfTwoArraysRev1().test(A, B, expected)
         }
     }
+
+    @Nested
+    inner class FindPrefixCommonArrayOfTwoArraysRev2Test {
+
+        @ParameterizedTest
+        @ArgumentsSource(InputArgumentsProvider::class)
+        fun `should return the prefix common array of A and B`(A: IntArray, B: IntArray, expected: IntArray) {
+            FindPrefixCommonArrayOfTwoArraysRev2().test(A, B, expected)
+        }
+    }
 }
 
 private fun FindPrefixCommonArrayOfTwoArrays.test(A: IntArray, B: IntArray, expected: IntArray) {