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  • 排序(Java 实现)

    冒泡排序:两两比较相邻记录的值,如果反序则交换,直到没有反序的记录为止。

    public void bubbleSort(int[] a) {
        boolean notSorted = true;
        for (int i = 0; i < a.length - 1 && notSorted; i++) {
            notSorted = false;
            for (int j = a.length - 2; j >= i; j--) {
                if (a[j] > a[j + 1]) { swap(a, j, j + 1); notSorted = true; }
            }
        }
    }
    

    ### 选择排序:通过n-i次值的比较,从n-i+1个记录中选出值最小的记录,并和第i个记录交换。
    public void selectionSort(int[] a) {
        for (int i = 0, min = 0; i < a.length - 1; i++) {
            min = i;
            for (int j = i + 1; j < a.length; j++) {
                if (a[j] < a[min]) min = j;
            }
            if (min != i) swap(a, min, i);
        }
    }
    

    ### 插入排序:将一个记录插入到已经排好序的有序表中。
    public void insertionSort(int[] a) {
        int temp;
        
        for (int i = 1, j; i < a.length; i++) {
            if (a[i] < a[i - 1]) {
                temp = a[i];
                for (j = i - 1; j >= 0 && a[j] > temp; j--)
                    a[j + 1] = a[j];
                a[j + 1] = temp;
        }
    }
    

    ### 归并排序:将两个或两个以上的有序表组合成一个新的有序表(递归)。
    public viod mergeSort(int[] a) {
        int[] temp = new int[a.length];
        mergeSort(a, temp, 0, a.length - 1);
    }
    
    private void mergeSort(int[] a, int[] temp, int low, int high) {
        if (low < high) {
            int mid = (low + high) / 2;
            mergeSort(a, temp, low, mid);
            mergeSort(a, temp, mid + 1, high);
            merge(a, temp, low, mid, high);
        }
    }
    
    private void merge(int[] a, int[] temp, int low, int mid, int high) {
        for (int i = low, i <= high; i++) {
            temp[i] = a[i];
        }
    
        int tempLeft = low;
        int tempRight = mid + 1;
        int current = low;
        while (tempLeft <= mid && tempRight <= high) {
            if (temp[tempLeft] <= temp[tempRight]) {
                a[current] = temp[tempLeft];
                tempLeft++;
            } else {
                a[current] = temp[tempRight];
                tempRight++;
            }
            current++;
        }
    
        int remaining = mid - tempLeft;
        for (int i = 0; i <= remaining; i++) {
            a[current + i] = temp[tempLeft + i];
        }
    }
    

    ### 快速排序:通过一趟排序将待排序记录分割成独立的两部分,其中一部分的值均比另一部分的值小,然后递归的对这两部分进行排序。
    public void quickSort(int[] a) {
        quickSort(a, 0, a.length - 1);
    }
    
    private void quickSort(int[] a, int low, int high) {
        if (low < high) {
            int p = partition(a, low, high);
            quickSort(a, low, p - 1);
            quickSort(a, p + 1, high);
        }
    }
    
    private int partition(int[] a, int low, int high) {
        int pivot = a[high];
        int i = low;
        for (int j = low; j <= high - 1; j++) {
            if (a[j] <= pivot) { swap(a, i, j); i++; }
        }
        swap(a, i, high);
        return i;
    }
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  • 原文地址:https://www.cnblogs.com/hippiebaby/p/5469169.html
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