算法

1.冒泡排序

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

    public static void main(String[] args) {
        int [] arrays  = {1,6, 9 ,4,2,3};
        int[] sortArrays = bubbleSort(arrays);
        System.out.println(Arrays.toString(sortArrays));
    }

2.选择排序

// 选择排序
    public static int [] selectSort(int arr[]){
        int n = arr.length;

        for(int i = 0; i<n - 1; i++){
            int minIndex = i;
            for(int j = i+1; j< n; j++){
                if(arr[j]<arr[minIndex]){
                    minIndex = j;
                }
            }
            int temp = arr[i];
            arr[i] = arr[minIndex];
            arr[minIndex] = temp;
        }
        return arr;
    }
    public static void main(String[] args) {
        int [] arrays  = { 1, 3, 6,4,7,12,5,1,2};
        int[] arraysSort = selectSort(arrays);
        System.out.println(Arrays.toString(arraysSort));
    }

3.插入排序

// 插入排序
    public static  int [] insertSort (int [] arr){
        int n = arr.length;
        for (int i = 1; i < n; i++) {
            int key = arr[i];
            int j = i-1;
            while (j>=0 && arr[j]> key){
                arr[j+1] = arr[j];
                j--;
            }
            arr[j+1] = key;
        }
        return arr;
    }

    public static void main(String[] args) {
        int [] arrays = {2,5,3,9,4,1};
        int[]  arraysSort= insertSort(arrays);
        System.out.println(Arrays.toString(arraysSort));
    }

4.两数之和

// 两数之和
    public static Integer [] twoSum(Integer[] nums , Integer target){
        HashMap<Integer, Integer> map = new HashMap<>();
        for (int i = 0; i < nums.length; i++) {
            if(map.containsKey(target - nums[i])){
                return new Integer[] {map.get(target - nums[i]),i};
            }
            map.put(nums[i],i);
        }
        throw new IllegalArgumentException( "");
    }
    public static void main(String[] args) {
        Integer  [] arr = {2,7,11,15};
        Integer target = 17;
        Integer[] index = twoSum(arr, target);
        System.out.println(Arrays.toString(index));
    }

5.回文数