Java数组操作 #

import java.util.Arrays;

int[] arr = {3, 1, 4, 1, 5, 9};
System.out.println(Arrays.toString(arr));
// [3, 1, 4, 1, 5, 9]

int[][] arr = {{1, 2}, {3, 4}, {5, 6}};
System.out.println(Arrays.deepToString(arr));
// [[1, 2], [3, 4], [5, 6]]

int[] arr = {3, 1, 4, 1, 5, 9, 2, 6};
Arrays.sort(arr);
System.out.println(Arrays.toString(arr));
// [1, 1, 2, 3, 4, 5, 6, 9]

int[] arr = {3, 1, 4, 1, 5, 9, 2, 6};
Arrays.sort(arr, 2, 6);  // 排序索引[2, 6)的元素
System.out.println(Arrays.toString(arr));
// [3, 1, 1, 4, 5, 9, 2, 6]

String[] names = {"Charlie", "Alice", "Bob"};
Arrays.sort(names);
System.out.println(Arrays.toString(names));
// [Alice, Bob, Charlie]

Integer[] arr = {3, 1, 4, 1, 5, 9};

// 降序排序
Arrays.sort(arr, (a, b) -> b - a);
System.out.println(Arrays.toString(arr));
// [9, 5, 4, 3, 1, 1]

// 或使用Comparator
Arrays.sort(arr, Comparator.reverseOrder());

int[] arr = {1, 2, 3, 4, 5, 6, 7, 8, 9};
int index = Arrays.binarySearch(arr, 5);
System.out.println(index);  // 4

// 未找到返回负数
int index2 = Arrays.binarySearch(arr, 10);
System.out.println(index2);  // -10（负数表示不存在）

// 数组必须已排序
int[] arr = {3, 1, 4, 1, 5};
Arrays.sort(arr);  // 先排序
int index = Arrays.binarySearch(arr, 4);
System.out.println(index);  // 3

int[] arr = {1, 2, 3, 4, 5, 6, 7, 8, 9};
int index = Arrays.binarySearch(arr, 2, 6, 5);  // 在索引[2,6)范围内查找
System.out.println(index);  // 4

int[] arr = {1, 2, 3, 4, 5};

// 复制指定长度
int[] copy1 = Arrays.copyOf(arr, 3);   // [1, 2, 3]
int[] copy2 = Arrays.copyOf(arr, 10);  // [1, 2, 3, 4, 5, 0, 0, 0, 0, 0]

int[] arr = {1, 2, 3, 4, 5};

// 复制指定范围 [from, to)
int[] copy = Arrays.copyOfRange(arr, 1, 4);
System.out.println(Arrays.toString(copy));  // [2, 3, 4]

int[] src = {1, 2, 3, 4, 5};
int[] dest = new int[5];

System.arraycopy(src, 0, dest, 0, src.length);
System.out.println(Arrays.toString(dest));  // [1, 2, 3, 4, 5]

// 参数：源数组, 源起始位置, 目标数组, 目标起始位置, 复制长度

int[] arr = {1, 2, 3, 4, 5};
int[] copy = arr.clone();
System.out.println(Arrays.toString(copy));  // [1, 2, 3, 4, 5]

int[] arr = new int[5];

// 填充所有元素
Arrays.fill(arr, 100);
System.out.println(Arrays.toString(arr));  // [100, 100, 100, 100, 100]

int[] arr = new int[5];

// 填充指定范围 [from, to)
Arrays.fill(arr, 1, 4, 50);
System.out.println(Arrays.toString(arr));  // [0, 50, 50, 50, 0]

int[] arr1 = {1, 2, 3};
int[] arr2 = {1, 2, 3};
int[] arr3 = {1, 2, 4};

System.out.println(Arrays.equals(arr1, arr2));  // true
System.out.println(Arrays.equals(arr1, arr3));  // false

int[][] arr1 = {{1, 2}, {3, 4}};
int[][] arr2 = {{1, 2}, {3, 4}};
int[][] arr3 = {{1, 2}, {3, 5}};

System.out.println(Arrays.deepEquals(arr1, arr2));  // true
System.out.println(Arrays.deepEquals(arr1, arr3));  // false

int[] arr = {1, 2, 3, 4, 5};

// 转为流
int sum = Arrays.stream(arr).sum();
System.out.println(sum);  // 15

// 过滤
int[] filtered = Arrays.stream(arr)
                       .filter(x -> x > 2)
                       .toArray();
System.out.println(Arrays.toString(filtered));  // [3, 4, 5]

int[] arr = {1, 2, 3, 4, 5};

int sum = Arrays.stream(arr).parallel().sum();
System.out.println(sum);  // 15

String[] arr = {"A", "B", "C"};
List<String> list = Arrays.asList(arr);
System.out.println(list);  // [A, B, C]

// 注意：返回的List是固定大小的
// list.add("D");  // UnsupportedOperationException

int[] arr = new int[5];

// 使用生成器设置值
Arrays.setAll(arr, i -> i * 2);
System.out.println(Arrays.toString(arr));  // [0, 2, 4, 6, 8]

// 并行设置
Arrays.parallelSetAll(arr, i -> i * i);
System.out.println(Arrays.toString(arr));  // [0, 1, 4, 9, 16]

int[] arr = {5, 3, 8, 1, 9, 2, 7, 4, 6};

Arrays.parallelSort(arr);
System.out.println(Arrays.toString(arr));
// [1, 2, 3, 4, 5, 6, 7, 8, 9]

public static void bubbleSort(int[] arr) {
    for (int i = 0; i < arr.length - 1; i++) {
        for (int j = 0; j < arr.length - 1 - i; j++) {
            if (arr[j] > arr[j + 1]) {
                int temp = arr[j];
                arr[j] = arr[j + 1];
                arr[j + 1] = temp;
            }
        }
    }
}

public static void selectionSort(int[] arr) {
    for (int i = 0; i < arr.length - 1; i++) {
        int minIndex = i;
        for (int j = i + 1; j < arr.length; j++) {
            if (arr[j] < arr[minIndex]) {
                minIndex = j;
            }
        }
        if (minIndex != i) {
            int temp = arr[i];
            arr[i] = arr[minIndex];
            arr[minIndex] = temp;
        }
    }
}

public static int linearSearch(int[] arr, int target) {
    for (int i = 0; i < arr.length; i++) {
        if (arr[i] == target) {
            return i;
        }
    }
    return -1;
}

public static int binarySearch(int[] arr, int target) {
    int left = 0, right = arr.length - 1;
    
    while (left <= right) {
        int mid = left + (right - left) / 2;
        
        if (arr[mid] == target) {
            return mid;
        } else if (arr[mid] < target) {
            left = mid + 1;
        } else {
            right = mid - 1;
        }
    }
    return -1;
}