c++ - 我的插入方法和binsearch方法有问题吗？

Question

我正在学习编程，并且已经创建了一个 void merge() 程序。我尝试添加二进制搜索方法和插入方法。该程序应按升序输出数组 A 和 B 的组合元素列表。 A 的元素应该放在B 的元素中。输出错误。

这是我的输出:

3 16
Inserting 512 into b at -1
2 0
61 154 170 275 426 509 612 653 677 703 765 897 908 512 503 512

这是我的代码:

#include<iostream>
#include<cmath>
using namespace std;

int binsearch(int array[], int first, int last, int search_key)
{
    int index;

    if (first > last)
        index = -1;

    else
    {
        int mid = (first + last) / 2;

        if (search_key == array[mid])
            index = mid;
        else

            if (search_key < array[mid])
                index = binsearch(array, first, mid - 1, search_key);
            else
                index = binsearch(array, mid + 1, last, search_key);

    } // end if
    return index;
}

void insert(int A[], int B[], int n, int m, int i){
    int j = n - m - 1, k = n - 1;
    while (i >= 0 && j >= 0){
        if (A[i] > B[j]){
            B[k--] = A[i--];
        }
        else {
            B[k--] = B[j--];
        }
    }
    if (j<0){
        while (i >= 0){
            B[k--] = A[i--];
        }
    }
}

void merge(int a[], int b[], int m, int n) {
    int a_size = m;
    int b_size = n;
    while (n != 0 && m != 0) {
        printf("%d %d\n", m, n);
        if (!(m > n)) {
            int t = log(n / m);
            int i = n + 1 - pow(2, t);
            if (a[m - 1] < b[i - 1]) {
                printf("Decreasing n\n");
                n = n - pow(2, t);
            }
            else {
                int k = binsearch(b, i - 1, n, a[m - 1]) + 1;
                printf("Inserting %d into b at %d\n", a[m - 1], k - 1);
                insert(a, b, b_size, k-3, m-1);
                b_size++;
                m = m - 1;
                n = k;
            }
        }
        else /* m > n */ {
            int t = log(n / m);
            int i = m + 1 - pow(2, t);
            if (b[n - 1] < a[i - 1]) {
                printf("Decreasing m\n");
                m = m - pow(2, t);
            }
            else {
                /*int k = binsearch(i - 1, m, b[n - 1], a) + 1;*/
                int k = binsearch(a, i - 1, m, b[n - 1]) + 1;
                printf("Inserting %d into a at %d\n", b[n - 1], k - 1);
                insert(b, a, a_size, k-3, n-1);
                a_size++;
                n = n - 1;
                m = k;
            }
        }
    }
    printf("%d %d\n", m, n);
}

int main(){
    int m = 3;
    int n = 16;
    int A[] = { 87, 503, 512 };
    int B[] = { 61, 154, 170, 275, 426, 509, 612, 653, 677, 703, 765, 897, 908 };

    merge(A, B, m, n);

    for (int i = 0; i<n; i++){
        printf("%d ", B[i]);
    }

    system("pause>0");
    return 0;
}

这是程序的逻辑:

Preliminary: A is an array of integers of length m and B is an array of integers of length n. Also the elements from both arrays are distinct (from the elements in both arrays) and in ascending order.

Step 1: if n or m is zero STOP. Otherwise if m>n, set t = [log (m/n)] and go to Step 4, else set t = [log (n/m)].

Step 2: compare A[m] with B[n + 1 – 2^t]. If A[m] is smaller, set n = n – 2^t and return to Step1.

Step 3: using binary search (which requires exactly t more comparisons), insert A[m] into its proper place among B[n + 1 - 2^t ] ... B[n]. If k is maximal such that B[k] < A[m], set m = m - 1 and n = k. Return to Step1.

Step 4: (Step 4 and 5 are like 2 and 4, interchanging the roles of n and m, A and B) if B[n] < A[m+1-2^t ], set m := m - 2^t and return to Step 1.

Step 5: insert B[n] into its proper place among the A’s. If k is maximal such that A[k] < B[n], set m = k and n = n - 1. Return to Step1.

Answer 1

一个问题是因为 binsearch。我认为你用错了。 binsearch 如果找不到元素，则返回 -1，否则返回该元素在数组中的索引。而且我认为你的 binsearch 版本就我所见和测试的而言正是这样做的。
您正在另一个数组(B 或 A)中搜索一个数组(A 或 B)的元素) 。 binsearch 返回 -1，因为 A 和 B 不同。 k 总是返回 -1。

在 C/C++ 中数组是固定大小的。大小一旦确定就不能更改。 A 的大小是 3，B 的大小是 13。增加数组的大小是错误的。

---

附录

Binsearch 实验

#include<iostream>
#include<cmath>

using namespace std;

/* binsearch from The C Programming Language (Second Edition) */
int binsearch1(int search_val, int array[], int array_len) {

    int low, high, mid;

    low = 0;
    high = array_len - 1;

    while (low <= high) {
        mid = (low + high) / 2;
        if (search_val < array[mid])
            high = mid - 1;
        else if (search_val > array[mid])
            low = mid + 1;
        else
            return mid;
    }

    return -1; /* no match */
}

/* binsearch from SO question: http://stackoverflow.com/q/34246941/1566187 */
int binsearch2(int array[], int first, int last, int search_key) {
    int index;

    if (first > last)
        index = -1;

    else {
        int mid = (first + last) / 2;

        if (search_key == array[mid])
            index = mid;
        else

            if (search_key < array[mid])
            index = binsearch2(array, first, mid - 1, search_key);
        else
            index = binsearch2(array, mid + 1, last, search_key);

    }
    return index;
}


/*
 * Comparing binsearch from reference book and So question
 */
int main() {
    int m = 3;
    int A[] = {87, 503, 512};

    int i = binsearch1(503, A, m);
    int j = binsearch2(A, 0, m - 1, 503);

    cout << "Elements are found at indices" << endl;
    cout << i << ", " << j << endl;

    i = binsearch1(99, A, m);
    j = binsearch2(A, 0, m - 1, 99);

    cout << "Element are not found, thus return is -1" << endl;
    cout << i << ", " << j << endl;

    return 0;
}