JAVA刷题之数组的总结和思路分享

public class ArraySummary {
    // 方法1：使用Arrays.sort()对数组进行排序
    public static void sortArray(int[] nums) {
        Arrays.sort(nums);
    }
 
    // 方法2：使用PriorityQueue实现堆排序，获取最大或最小的k个元素
    public static int[] getLeastNumbers(int[] arr, int k) {
        if (k == 0 || arr.length == 0) return new int[0];
        
        PriorityQueue<Integer> maxHeap = new PriorityQueue<>((a, b) -> b - a);
        
        for (int num : arr) {
            if (maxHeap.size() < k) {
                maxHeap.offer(num);
            } else if (num < maxHeap.peek()) {
                maxHeap.poll();
                maxHeap.offer(num);
            }
        }
        
        int[] leastNumbers = new int[k];
        for (int i = 0; i < k; i++) {
            leastNumbers[i] = maxHeap.poll();
        }
        return leastNumbers;
    }
 
    // 方法3：使用HashSet去重
    public static int[] removeDuplicates(int[] nums) {
        HashSet<Integer> set = new HashSet<>();
        int writeIndex = 0;
        for (int num : nums) {
            if (!set.contains(num)) {
                set.add(num);
                nums[writeIndex++] = num;
            }
        }
        return Arrays.copyOf(nums, writeIndex);
    }
 
    // 方法4：使用双指针找出数组中的最大子数组和
    public static int maxSubArray(int[] nums) {
        int maxSum = nums[0], currentSum = maxSum;
        for (int i = 1; i < nums.length; i++) {
            currentSum = Math.max(nums[i], currentSum + nums[i]);
            maxSum = Math.max(maxSum, currentSum);
        }
        return maxSum;
    }
 
    public static void main(String[] args) {
        // 测试sortArray
        int[] nums = {3, 1, 2, 4, 5};
        sortArray(nums);
        System.out.println(Arrays.toString(nums)); // 输出 [1, 2, 3, 4, 5]
 
        // 测试getLeastNumbers
        int[] arr = {3, 2, 1, 5, 6, 4};
        int k = 3;
        int[] leastNumbers = getLeastNumbers(arr, k);
        System.out.println(Arrays.toString(leastNumbers)); // 输出 [1, 2, 3]
 
        // 测试removeDuplicates
        int[] duplicateNums = {1, 1, 2, 3, 3, 3};
        int[] uniqueNums = removeDuplicates(duplicateNums);
        System.out.println(Arrays.toString(uniqueNums)); // 输出 [1, 2, 3]
 
        // 测试maxSubArray
        int[] sumNums = {-2, 1, -3, 4