排序

冒泡排序

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

选择排序

public static void selectionSort(int[] arr) {
        int temp, min = 0;
        for (int i = 0; i < arr.length - 1; i++) {
            min = i;
            // 循环查找最小值
            for (int j = i + 1; j < arr.length; j++) {
                if (arr[min] > arr[j]) {
                    min = j;
                }
            }
            if (min != i) {
                temp = arr[i];
                arr[i] = arr[min];
                arr[min] = temp;
            }
        }
    }

插入排序

public static void insertionSort(int[] arr){
    for (int i=1; i<arr.length; ++i){
        int value = arr[i];
        int position=i;
        while (position>0 && arr[position-1]>value){
            arr[position] = arr[position-1];
            position--;
        }
        arr[position] = value;
    }//loop i
}

归并排序

    public static void mergeSort(int[] arr, int left, int right, int[] temp) {
        if (left < right) {
            //中间索引
            int mid = (left + right) / 2;
            //向左递归进行分解
            //0 - mid 即是0 - 3 {8,4,5,7}
            mergeSort(arr, left, mid, temp);
            //向右递归进行分解
            //mid+1 - midright 即是4 - 7  {1,3,6,2}
            mergeSort(arr, mid + 1, right, temp);
            //进行合并
            merge(arr, left, mid, right, temp);
        }
    }
    public static void merge(int[] arr, int left, int mid, int right, int[] temp) {
        int i = left;
        int j = mid + 1;
        int k = 0;
        while (i <= mid && j <= right) {
            temp[k++] = arr[i] <= arr[j] ? arr[i++] : arr[j++];
        }
        while (i <= mid) {
            temp[k++] = arr[i++];
        }
        while (j <= right) {
            temp[k++] = arr[j++];
        }
        //把数据复制回原数组
        for (i = 0; i < k; ++i) {
            arr[left + i] = temp[i];
        }
    }