From d7d53d5fa004dfafca0322fb2f793f35cacd3df6 Mon Sep 17 00:00:00 2001
From: Leonid <l.khristyuk@smartagro.ru>
Date: Wed, 7 May 2025 10:05:18 +0300
Subject: [PATCH] =?UTF-8?q?=D0=98=D1=81=D0=BF=D1=80=D0=B0=D0=B2=D0=B8?=
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---
 .../service/ExcelProcessorService.java        |  4 ---
 .../excelprocessor/util/QuickSelect.java      | 25 ++++++++++++++++---
 2 files changed, 21 insertions(+), 8 deletions(-)

diff --git a/src/main/java/com/example/excelprocessor/service/ExcelProcessorService.java b/src/main/java/com/example/excelprocessor/service/ExcelProcessorService.java
index d673b81..d764e5b 100644
--- a/src/main/java/com/example/excelprocessor/service/ExcelProcessorService.java
+++ b/src/main/java/com/example/excelprocessor/service/ExcelProcessorService.java
@@ -20,10 +20,6 @@ public class ExcelProcessorService {
     public Integer findNthSmallest(MultipartFile file, int n) throws IOException {
 
         List<Integer> numbers = excelReader.readNumbersFromFirstColumn(file);
-
-        if (n < 1 || n > numbers.size()) {
-            throw new IllegalArgumentException("Некорректный порядковый номер N");
-        }
         return QuickSelect.findNthSmallest(numbers, n);
     }
 }
\ No newline at end of file
diff --git a/src/main/java/com/example/excelprocessor/util/QuickSelect.java b/src/main/java/com/example/excelprocessor/util/QuickSelect.java
index f2fcfe6..c7d11da 100644
--- a/src/main/java/com/example/excelprocessor/util/QuickSelect.java
+++ b/src/main/java/com/example/excelprocessor/util/QuickSelect.java
@@ -1,15 +1,30 @@
 package com.example.excelprocessor.util;
 
-import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.Objects;
+import java.util.Random;
 
-public class QuickSelect {
+public final class QuickSelect {
+
+    private static final Random random = new Random();
 
     public static int findNthSmallest(List<Integer> numbers, int n) {
 
-        List<Integer> copyList = new ArrayList<>(numbers);
-        return quickSelect(copyList, 0, copyList.size() - 1, n - 1);
+        validateNumbersNotEmpty(numbers);
+
+        if (n < 1 || n > numbers.size()) {
+            throw new IllegalArgumentException("Некорректный порядковый номер N");
+        }
+
+        return quickSelect(numbers, 0, numbers.size() - 1, n - 1);
+    }
+
+    private static void validateNumbersNotEmpty(List<Integer> numbers) {
+
+        if (Objects.isNull(numbers) || numbers.isEmpty()) {
+            throw new IllegalArgumentException("Список не может быть пустым");
+        }
     }
 
     private static int quickSelect(List<Integer> numbers, int from, int to, int n) {
@@ -31,6 +46,8 @@ public class QuickSelect {
 
     private static int partition(List<Integer> list, int from, int to) {
 
+        int pivotIdx = from + random.nextInt(to - from + 1);
+        Collections.swap(list, pivotIdx, to);
         int currIdx = from;
         int pivot = list.get(to);