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Add another method to find kth number (#5918)

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This commit is contained in:
Taranjeet Singh Kalsi
2024-10-26 16:56:01 +05:30
committed by GitHub
parent 871e4df0d9
commit 95875b0ae4
2 changed files with 30 additions and 0 deletions
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17
src/main/java/com/thealgorithms/maths/FindKthNumber.java
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@ -1,5 +1,7 @@
package com.thealgorithms.maths; package com.thealgorithms.maths;
import java.util.Collections;
import java.util.PriorityQueue;
import java.util.Random; import java.util.Random;
/** /**
@ -62,4 +64,19 @@ public final class FindKthNumber {
array[i] = array[j]; array[i] = array[j];
array[j] = temp; array[j] = temp;
} }
public static int findKthMaxUsingHeap(int[] array, int k) {
if (k <= 0 || k > array.length) {
throw new IllegalArgumentException("k must be between 1 and the size of the array");
}
PriorityQueue<Integer> maxHeap = new PriorityQueue<>(Collections.reverseOrder()); // using max-heap to store numbers.
for (int num : array) {
maxHeap.add(num);
}
while (k > 1) {
maxHeap.poll(); // removing max number from heap
k--;
}
return maxHeap.peek();
}
} }

13
src/test/java/com/thealgorithms/maths/FindKthNumberTest.java
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@ -14,21 +14,30 @@ public class FindKthNumberTest {
assertEquals(3, FindKthNumber.findKthMax(array1, 3)); assertEquals(3, FindKthNumber.findKthMax(array1, 3));
assertEquals(4, FindKthNumber.findKthMax(array1, 2)); assertEquals(4, FindKthNumber.findKthMax(array1, 2));
assertEquals(5, FindKthNumber.findKthMax(array1, 1)); assertEquals(5, FindKthNumber.findKthMax(array1, 1));
assertEquals(3, FindKthNumber.findKthMaxUsingHeap(array1, 3));
assertEquals(4, FindKthNumber.findKthMaxUsingHeap(array1, 2));
assertEquals(5, FindKthNumber.findKthMaxUsingHeap(array1, 1));
int[] array2 = {7, 5, 8, 2, 1, 6}; int[] array2 = {7, 5, 8, 2, 1, 6};
assertEquals(5, FindKthNumber.findKthMax(array2, 4)); assertEquals(5, FindKthNumber.findKthMax(array2, 4));
assertEquals(6, FindKthNumber.findKthMax(array2, 3)); assertEquals(6, FindKthNumber.findKthMax(array2, 3));
assertEquals(8, FindKthNumber.findKthMax(array2, 1)); assertEquals(8, FindKthNumber.findKthMax(array2, 1));
assertEquals(5, FindKthNumber.findKthMaxUsingHeap(array2, 4));
assertEquals(6, FindKthNumber.findKthMaxUsingHeap(array2, 3));
assertEquals(8, FindKthNumber.findKthMaxUsingHeap(array2, 1));
} }
@Test @Test
public void testFindKthMaxEdgeCases() { public void testFindKthMaxEdgeCases() {
int[] array1 = {1}; int[] array1 = {1};
assertEquals(1, FindKthNumber.findKthMax(array1, 1)); assertEquals(1, FindKthNumber.findKthMax(array1, 1));
assertEquals(1, FindKthNumber.findKthMaxUsingHeap(array1, 1));
int[] array2 = {5, 3}; int[] array2 = {5, 3};
assertEquals(5, FindKthNumber.findKthMax(array2, 1)); assertEquals(5, FindKthNumber.findKthMax(array2, 1));
assertEquals(3, FindKthNumber.findKthMax(array2, 2)); assertEquals(3, FindKthNumber.findKthMax(array2, 2));
assertEquals(5, FindKthNumber.findKthMaxUsingHeap(array2, 1));
assertEquals(3, FindKthNumber.findKthMaxUsingHeap(array2, 2));
} }
@Test @Test
@ -36,6 +45,8 @@ public class FindKthNumberTest {
int[] array = {1, 2, 3, 4, 5}; int[] array = {1, 2, 3, 4, 5};
assertThrows(IllegalArgumentException.class, () -> FindKthNumber.findKthMax(array, 0)); assertThrows(IllegalArgumentException.class, () -> FindKthNumber.findKthMax(array, 0));
assertThrows(IllegalArgumentException.class, () -> FindKthNumber.findKthMax(array, 6)); assertThrows(IllegalArgumentException.class, () -> FindKthNumber.findKthMax(array, 6));
assertThrows(IllegalArgumentException.class, () -> FindKthNumber.findKthMaxUsingHeap(array, 0));
assertThrows(IllegalArgumentException.class, () -> FindKthNumber.findKthMaxUsingHeap(array, 6));
} }
@Test @Test
@ -43,8 +54,10 @@ public class FindKthNumberTest {
int[] array = generateArray(1000); int[] array = generateArray(1000);
int k = new Random().nextInt(1, array.length); int k = new Random().nextInt(1, array.length);
int result = FindKthNumber.findKthMax(array, k); int result = FindKthNumber.findKthMax(array, k);
int maxK = FindKthNumber.findKthMaxUsingHeap(array, k);
Arrays.sort(array); Arrays.sort(array);
assertEquals(array[array.length - k], result); assertEquals(array[array.length - k], result);
assertEquals(array[array.length - k], maxK);
} }
public static int[] generateArray(int capacity) { public static int[] generateArray(int capacity) {