简单算法实现 java

• 冒泡排序

    //冒泡排序
    public static void demo(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 + 1];
                    arr[j + 1] = arr[j];
                    arr[j] = temp;
                }
            }
        }
        System.out.println(Arrays.toString(arr));
    }

• 选择排序

    //选择排序
    public static int[] xzDemo(int[] arr) {
        for (int i = 0; i < arr.length - 1; i++) {
            for (int j = i + 1; j < arr.length; j++) {
                if (arr[i] > arr[j]) {
                    int temp = arr[i];
                    arr[i] = arr[j];
                    arr[j] = temp;
                }
            }
        }
        return arr;
    }

• 二分查找 这个数组必须是排好序的(从大到小或者从小到大)  

    //二分查找
    public static int towDome(int[] arr, int key) {
        int left = 0;
        int right = arr.length - 1;
        while (left <= right) {
            int middle = (left + right) / 2;
            if (arr[middle] == key) {
                System.out.println(middle);
                return middle;
            } else if (arr[middle] > key) {
                right = middle - 1;
            } else {
                left = middle + 1;
            }
        }
        return -1;
    }