Algorithms4

发表于

2.Sorting

2.1 Elementary Sorts

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private static boolean less(Comparable v, Comparable w) {
   return (v.compareTo(w) < 0);
}
// v是否小于w

private static void exch(Comparable[] a, int i, int j) {
   Comparable swap = a[i];
   a[i] = a[j];
   a[j] = swap;
}
// swap

Selection sort

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public static void sort(Comparable[] a) {
    int n = a.length;
    for (int i = 0; i < n; i++) {
        int min = i;
        for (int j = i+1; j < n; j++) {
            if (less(a[j], a[min])) min = j;
        }
        exch(a, i, min);
    }
}

Insertion sort

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public static void sort(Comparable[] a) {
    int n = a.length;
    for (int i = 1; i < n; i++) {
        for (int j = i; j > 0 && less(a[j], a[j-1]); j--) {
            exch(a, j, j-1);
        }
    }
}

Shellsort

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public static void sort(Comparable[] a) {
    int n = a.length;

    // 3x+1 increment sequence:  1, 4, 13, 40, 121, 364, 1093, ...
    int h = 1;
    while (h < n/3) h = 3*h + 1;

    while (h >= 1) {
        // h-sort the array
        for (int i = h; i < n; i++) {
            for (int j = i; j >= h && less(a[j], a[j-h]); j -= h) {
                exch(a, j, j-h);
            }
        }
        h /= 3;
    }
}