排序算法

---恢复内容开始---

## 参数检查 ## ``` /** * 检查参数 * * @param a * @param * @return */ private static > boolean isEmpty(T[] a) { return a == null || a.length == 0; } ``` ## 选择排序 ## ``` /** * 选择排序 * * @param a * @param */ public static > void selectSort(T[] a) { if (isEmpty(a)) throw new IllegalArgumentException(); int n = a.length; for (int i = 0; i < n; i++) { T tmp = a[i]; int min = i; for (int j = i + 1; j < n; j++) { if (a[j].compareTo(a[min]) < 0) min = j; } a[i] = a[min]; a[min] = tmp; } } ``` ## 插入排序 ## ``` /** * 插入排序 * * @param a * @param */ public static > void insertionSort(T[] a) { if (isEmpty(a)) throw new IllegalArgumentException(); int j; for (int i = 1; i < a.length; i++) { T tmp = a[i]; for (j = i; j > 0 && tmp.compareTo(a[j - 1]) < 0; j--) { a[j] = a[j - 1]; } a[j] = tmp; } } ``` ## 希尔排序 ## ``` /** * 希尔排序 * * @param a * @param */ public static > void shellSort(T[] a) { if (isEmpty(a)) throw new IllegalArgumentException(); int j; for (int gap = a.length / 2; gap > 0; gap /= 2) { for (int i = gap; i < a.length; i++) { T tmp = a[i]; for (j = i; j >= gap && tmp.compareTo(a[j - gap]) < 0; j -= gap) { a[j] = a[j - gap]; } a[j] = tmp; } } } ``` ## 归并排序 ## ``` /** * 递归的归并排序 * * @param a * @param */ public static > void mergeSort(T[] a) { if (isEmpty(a)) throw new IllegalArgumentException(); T[] tmp = (T[]) new Comparable[a.length]; mergeSort(a, tmp, 0, a.length - 1); }

/**
 * 自底向上的归并
 *
 * @param a
 * @param <T>
 */
public static <T extends Comparable<? super T>> void mergeSort2(T[] a) {
    if (isEmpty(a)) throw new IllegalArgumentException();
    int N = a.length;
    T[] tmp = (T[]) new Comparable[N];
    for (int sz = 1; sz < N; sz += sz) {
        for (int lo = 0; lo < N - sz; lo += sz + sz) {
            merge(a, tmp, lo, lo + sz - 1, Math.min(lo + sz + sz - 1, N - 1));
        }
    }
}

private static <T extends Comparable<? super T>> void mergeSort(T[] a, T[] tmp, int left, int right) {
    if (left < right) {
        int center = (left + right) / 2;
        mergeSort(a, tmp, left, center);
        mergeSort(a, tmp, center + 1, right);
        merge(a, tmp, left, center, right);
    }
}

private static <T extends Comparable<? super T>> void merge(T[] a, T[] tmp, int lo, int mid, int hi) {
    int i = lo;
    int j = mid + 1;

    for (int k = lo; k <= hi; k++) tmp[k] = a[k];

    for (int k = lo; k <= hi; k++) {
        if (i > mid) a[k] = tmp[j++];
        else if (j > hi) a[k] = tmp[i++];
        else if (tmp[j].compareTo(tmp[i]) < 0) a[k] = tmp[j++];
        else a[k] = tmp[i++];
    }
}

## 快速排序 ##

/**
 * 快速排序
 *
 * @param a
 * @param <T>
 */
public static <T extends Comparable<? super T>> void quickSort(T[] a) {
    if (isEmpty(a)) throw new IllegalArgumentException();
    quickSort(a, 0, a.length - 1);
}

private static <T extends Comparable<? super T>> void quickSort(T[] a, int lo, int hi) {
    if (lo < hi) {
        int index = partition(a, lo, hi);
        quickSort(a, lo, index - 1);
        quickSort(a, index + 1, hi);
    }
}

private static <T extends Comparable<? super T>> int partition(T[] a, int lo, int hi) {
    T tmp = a[lo];
    while (lo < hi) {
        while (lo < hi && a[hi].compareTo(tmp) >= 0) hi--;
        a[lo] = a[hi];
        while (lo < hi && a[lo].compareTo(tmp) <= 0) lo++;
        a[hi] = a[lo];
    }
    a[lo] = tmp;
    return lo;
}

## 堆排序 ##

/**
 * 堆排序
 *
 * @param a
 * @param <T>
 */
public static <T extends Comparable<? super T>> void heapSort(T[] a) {
    if (isEmpty(a)) throw new IllegalArgumentException();
    for (int i = a.length / 2; i >= 0; i--) percDown(a, i, a.length);
    for (int i = a.length - 1; i > 0; i--) {
        T tmp = a[0];
        a[0] = a[i];
        a[i] = tmp;
        percDown(a, 0, i);
    }
}

private static <T extends Comparable<? super T>> void percDown(T[] a, int i, int n) {
    int child;
    T tmp;
    for (tmp = a[i]; 2 * i < n - 1; i = child) {
        child = 2 * i + 1;
        if (child != n - 1 && a[child].compareTo(a[child + 1]) < 0) child++;
        if (tmp.compareTo(a[child]) < 0) {
            a[i] = a[child];
        } else {
            break;
        }
    }
    a[i] = tmp;
}

 /**
 * 检查参数
 *
 * @param a
 * @param <T>
 * @return
 */
private static <T extends Comparable<? super T>> boolean isEmpty(T[] a) {
    return a == null || a.length == 0;
}

## 选择排序 ##

/**
 * 选择排序
 *
 * @param a
 * @param <T>
 */
public static <T extends Comparable<? super T>> void selectSort(T[] a) {
    if (isEmpty(a)) throw new IllegalArgumentException();
    int n = a.length;
    for (int i = 0; i < n; i++) {
        T tmp = a[i];
        int min = i;
        for (int j = i + 1; j < n; j++) {
            if (a[j].compareTo(a[min]) < 0) min = j;
        }
        a[i] = a[min];
        a[min] = tmp;
    }
}

## 插入排序 ##

/**
 * 插入排序
 *
 * @param a
 * @param <T>
 */
public static <T extends Comparable<? super T>> void insertionSort(T[] a) {
    if (isEmpty(a)) throw new IllegalArgumentException();
    int j;
    for (int i = 1; i < a.length; i++) {
        T tmp = a[i];
        for (j = i; j > 0 && tmp.compareTo(a[j - 1]) < 0; j--) {
            a[j] = a[j - 1];
        }
        a[j] = tmp;
    }
}

## 希尔排序 ##

/**
 * 希尔排序
 *
 * @param a
 * @param <T>
 */
public static <T extends Comparable<? super T>> void shellSort(T[] a) {
    if (isEmpty(a)) throw new IllegalArgumentException();
    int j;
    for (int gap = a.length / 2; gap > 0; gap /= 2) {
        for (int i = gap; i < a.length; i++) {
            T tmp = a[i];
            for (j = i; j >= gap && tmp.compareTo(a[j - gap]) < 0; j -= gap) {
                a[j] = a[j - gap];
            }
            a[j] = tmp;
        }
    }
}

## 归并排序 ##

/**
 * 递归的归并排序
 *
 * @param a
 * @param <T>
 */
public static <T extends Comparable<? super T>> void mergeSort(T[] a) {
    if (isEmpty(a)) throw new IllegalArgumentException();
    T[] tmp = (T[]) new Comparable[a.length];
    mergeSort(a, tmp, 0, a.length - 1);
}

/**
 * 自底向上的归并
 *
 * @param a
 * @param <T>
 */
public static <T extends Comparable<? super T>> void mergeSort2(T[] a) {
    if (isEmpty(a)) throw new IllegalArgumentException();
    int N = a.length;
    T[] tmp = (T[]) new Comparable[N];
    for (int sz = 1; sz < N; sz += sz) {
        for (int lo = 0; lo < N - sz; lo += sz + sz) {
            merge(a, tmp, lo, lo + sz - 1, Math.min(lo + sz + sz - 1, N - 1));
        }
    }
}

private static <T extends Comparable<? super T>> void mergeSort(T[] a, T[] tmp, int left, int right) {
    if (left < right) {
        int center = (left + right) / 2;
        mergeSort(a, tmp, left, center);
        mergeSort(a, tmp, center + 1, right);
        merge(a, tmp, left, center, right);
    }
}

private static <T extends Comparable<? super T>> void merge(T[] a, T[] tmp, int lo, int mid, int hi) {
    int i = lo;
    int j = mid + 1;

    for (int k = lo; k <= hi; k++) tmp[k] = a[k];

    for (int k = lo; k <= hi; k++) {
        if (i > mid) a[k] = tmp[j++];
        else if (j > hi) a[k] = tmp[i++];
        else if (tmp[j].compareTo(tmp[i]) < 0) a[k] = tmp[j++];
        else a[k] = tmp[i++];
    }
}

## 快速排序 ##

/**
 * 快速排序
 *
 * @param a
 * @param <T>
 */
public static <T extends Comparable<? super T>> void quickSort(T[] a) {
    if (isEmpty(a)) throw new IllegalArgumentException();
    quickSort(a, 0, a.length - 1);
}

private static <T extends Comparable<? super T>> void quickSort(T[] a, int lo, int hi) {
    if (lo < hi) {
        int index = partition(a, lo, hi);
        quickSort(a, lo, index - 1);
        quickSort(a, index + 1, hi);
    }
}

private static <T extends Comparable<? super T>> int partition(T[] a, int lo, int hi) {
    T tmp = a[lo];
    while (lo < hi) {
        while (lo < hi && a[hi].compareTo(tmp) >= 0) hi--;
        a[lo] = a[hi];
        while (lo < hi && a[lo].compareTo(tmp) <= 0) lo++;
        a[hi] = a[lo];
    }
    a[lo] = tmp;
    return lo;
}

## 堆排序 ##

/**
 * 堆排序
 *
 * @param a
 * @param <T>
 */
public static <T extends Comparable<? super T>> void heapSort(T[] a) {
    if (isEmpty(a)) throw new IllegalArgumentException();
    for (int i = a.length / 2; i >= 0; i--) percDown(a, i, a.length);
    for (int i = a.length - 1; i > 0; i--) {
        T tmp = a[0];
        a[0] = a[i];
        a[i] = tmp;
        percDown(a, 0, i);
    }
}

private static <T extends Comparable<? super T>> void percDown(T[] a, int i, int n) {
    int child;
    T tmp;
    for (tmp = a[i]; 2 * i < n - 1; i = child) {
        child = 2 * i + 1;
        if (child != n - 1 && a[child].compareTo(a[child + 1]) < 0) child++;
        if (tmp.compareTo(a[child]) < 0) {
            a[i] = a[child];
        } else {
            break;
        }
    }
    a[i] = tmp;
}