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[英]Why my C++ Graphics Program is not showing any output with g++ compiler?
[英]Why is this C++ program not showing any output?
我正在嘗試為二進制搜索編寫代碼,但它沒有顯示任何 output。 請告訴我我的錯誤。
#include <iostream>
using namespace std;
int main(){
int a[]= {1, 3, 5 , 7, 32};
int n;
cin>>n;
int last=(sizeof(a)/sizeof(a[0]))-1;
int first=0;
while(first<=last){
int mid=(last-1)/2;
if(a[mid]==n){
cout<<"No. Found"<< endl;
}
if(n>a[mid])
{
first=mid+1;
}
else
{
last=mid-1;
}
}
cout<<"Not Found"<<endl;
return 0;
}
你計算mid
的方式不對,應該是這樣的:
int mid = (first + last) / 2;
最好的方法是避免溢出( first + last
可以溢出):
int mid = first + (last - first) / 2;
或使用>>
運算符:
int mid = (first + last) >> 1;
您的二進制搜索代碼沒有產生任何 output 的原因是因為存在一些邏輯錯誤,例如:
您正在使用不正確的方法來查找中間值,找到中間值的適當方法是:
mid = (f1 + f2) / 2** (where f1 = first, f2 = last)
以下是更新后的二分搜索代碼,並附有一些有用的注釋:
#include <bits/stdc++.h>
using namespace std;
// A Iterative Binary Search Function.
int BinarySearch(int arr[], int low, int r, int x)
{
while (low <= r)
{
int mid = low + (r - low) / 2;
// To check whether int x is at mid or not.
if (arr[mid] == x)
{
return mid;
}
// If x is greater than mid value, ignore the left half
if (arr[mid] < x)
{
low = mid + 1;
}
// If x is smaller than mid-value, ignore the right half
else
{
r = mid - 1;
}
}
// if your desired element is not there
return -1;
}
int main(void)
{
int arr[] = {1, 3, 5, 7, 32};
int x;
cin >> x;
int n = sizeof(arr) / sizeof(arr[0]);
int result = binarySearch(arr, 0, n - 1, x);
if(result == -1)
{
cout << "Element is not present in array"
cout << "Element is present at index " << result << endl;
}
return 0;
}
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