排序

1、冒泡

public static void bubbleSort(int a[]) {
    int temp;
    boolean complete = true;
    for (int i = 1; i < a.length; i++) {
        complete = true;
        for (int j = 0; j < a.length - i; j++) {
             // 循環每次把最大的數放置在最後
            if (a[j] > a[j + 1]) {
               temp = a[j];
               a[j] = a[j + 1];
               a[j + 1] = temp;
               complete = false;
            }
            print(a);
        }
        if (complete) { // 表示前面的數已經都是按序列了。所以後面for循環已經沒有必要再執行了，能夠直接斷開
            break;
        }
    }
}

2、歸併

public static void merge_sort(int a[], int low, int high) {
    if (low < high) {
        int mid = (low + high) / 2;
        merge_sort(a, low, mid);
        merge_sort(a, mid + 1, high);
        merge(a, low, mid, high);
    }
}

public static void merge(int a[], int low, int mid, int high) {
    int temp[] = new int[high - low + 1];
    int k;
    int left_low = low;
    int left_high = mid;
    int right_low = mid + 1;
    int right_high = high;
    for (k = 0; left_low <= left_high && right_low <= right_high; k++) {
        if (a[left_low] <= a[right_low]) {
            temp[k] = a[left_low++];
        } else {
            temp[k] = a[right_low++];
        }
    }
    if (left_low <= left_high) {
        for (int i = left_low; i <= left_high; i++) {
            temp[k++] = a[i];
        }
    }
    if (right_low <= right_high) {
        for (int i = right_low; i <= right_high; i++) {
            temp[k++] = a[i];
        }
    }
    for (int i = 0; i < high - low + 1; i++) {
        a[low + i] = temp[i];
    }
}

3、快排

public static void quick_sort(int a[], int left, int right) {
    if (left < right) {
        int temp = a[left];
        int i = left, j = right;
        while (i < j) {
            while (i < j && a[j] >= temp) {
                j--;
            }
            if (i < j) {
                a[i] = a[j];
                i++;
            }
            while (i < j && a[i] <= temp) {
                i++;
            }
            if (i < j) {
                a[j] = a[i];
                j--;
            }
        }
        a[i] = temp;
        quick_sort(a, left, i - 1);
        quick_sort(a, i + 1, right);
    }
}