Question

我想找到排序数组中元素的出现次数。我使用BinarySearch逻辑来实现这一点。但我没有得到正确的输出。我正在使用这个逻辑

numberOfOccurrence = findLastOccurrence - firstOccurrence + 1

这是我的代码

#include<stdio.h>
int find_last(int a[],int n,int key)
{
    int low = 0;
    int high = n-1;
    int result = -1;
    while(low<=high)
    {
        int mid = (low+high)/2;
        if(a[mid]==key)
            {
                result = mid;
                low = mid+1;
            }
        else if(key<a[mid])
            high = mid-1;
        else 
            low = mid+1;
    }
    return result;
}
int find_first(int a[],int n,int key)
{
    int low = 0;
    int high = n-1;
    int result = -1;
    while(low<=high)
    {
        int mid = (low+high)/2;
        if(a[mid]==key)
            {
                result = mid;
                high = mid-1;
            }
        else if(key<a[mid])
            high = mid-1;
        else 
            low = mid+1;
    }
    return result;
}
int find_count(int a[],int n,int x)
{
    int first,last;
    first =  find_first(a,n,x);
    last = find_last(a,n,x);
    printf("\nLast index is %d",last+1);
    printf("\nFirst index is %d",first+1);
    printf("\nlast-first+1 is %d",last - first + 1);
    return (last-first+1);
}
main()
{
    int a[10],flag=0,n,x,count=0,i;
    printf("\nEnter the number of elements ");
    scanf("%d",&n);
    printf("\nEnter %d elements ",n);
    for(i=0;i<n;i++){
        scanf("%d",&a[i]);
    }   
    printf("\n Elements are \n");
    for(i=0;i<n;i++){
        printf("%d ",a[i]);
    }
    printf("\n Enter the key ");
    scanf("%d",&x);
    count = find_count(a,n,x);
    printf("%d","\n The count is %d \n",count);
}

但声明return (last-first+1);中有些问题。它返回了一些大的值。

我在使用mingw和Visual Studio 2010的CFree中进行了测试。

Answer 1

printf("%d","\n The count is %d \n",count);

将其更改为：

printf(" The count is %d \n",count);

你不能在printf

中放置多个“”

Answer 2

你甚至不需要二元搜索（在任何情况下都需要对数组进行排序）。无论是否对数组进行排序，都需要对数组进行简单的遍历。加上一个小错误检查好的形式（GIGO），这使得这个程序看起来比没有它更笨重。代码的关键部分只有3行。

#include<stdio.h>

#define NUMBERS 10

int main ( ) {
    int a[NUMBERS], n, x, count=0, i;

    printf("\nEnter the number of elements ");
    if (1 != scanf("%d",&n))
        return 1;                           // bad entry
    if (1 > n || NUMBERS < n)
        return 1;                           // number out of range

    printf("\nEnter %d elements ", n);
    for(i=0; i<n; i++){
        if (1 != scanf("%d", &a[i]))
        return 1;                           // illegal number
    }

    printf("\nElements are \n");
    for(i=0; i<n; i++){
        printf("%d ", a[i]);
    }

    printf("\nEnter the key ");
    if (1 != scanf("%d", &x))
        return 1;                           // bad entry

    for(i=0; i<n; i++){                     // <--- every element
        if (x == a[i])                      // <--- find matching key
            count++;                        // <--- keep a tally
    }

    printf("\nThe count is %d\n", count);   // (corrected) result
    return 0;
}

排序数组中元素的出现次数

2 个答案: