Question

我刚刚在课堂上学习二进制搜索，下面的代码只是一个例子，因为我试图更好地理解它。所以说这个代码是编译但不显示任何输出，因为我缺乏二进制搜索的知识，我不知道为什么没有任何输出。有人可以指出真正写好的教程的方向吗？或者帮助表明代码有什么问题。

#include "stdafx.h"
#include <iostream>
#include <iomanip>
#include <conio.h>
#include <vector>
#include <algorithm>

using namespace std;
int SIZE = 10;

int main()
{
    int thisArray[] = { 99,86,44,55,78,63,0,32,11 };
    int num = 0;

    int n = 0;

    int first;
    int last;
    int middle;
    first = 0;
    last = n - 1;
    middle = (first + last) / 2;
    cout << "Enter the total number of elements\n";
    cin >> n;

    cout << "Entered " << n << "number.\n";

    for (int i = 0; i < n; i++) {
        cin >> thisArray[i];
    }

    cout << "Enter a number to find.\n";
    cin >> num;

    while (first <= last) {
        if (thisArray[middle] < num) {
            first = middle + 1;
        }
        else if (thisArray[middle] == num ) {
            cout << num << " found at location " << middle + 1 << "\n";
            break;
        }
        else {
            last = middle - 1;
        }
        middle = (first + last) / 2;
    }


    return 0;
}

编辑：

#include "stdafx.h"
#include <iostream>
#include <iomanip>
#include <conio.h>
#include <vector>
#include <algorithm>

using namespace std;
int SIZE = 10;

int main()
{
    //this is my binary search
    int thisArray[10] = { 0,11,32,44,55,63,78,86,99 };
    int i = 0; //index of the array
    int n = 0; //variable of number that will be looked for
    int first = 0;
    int last = SIZE - 1;
    int middle;
    int pos = -1;
    bool found = false;
    int count = 0;
    while (found) {

        cout << "Enter a number to look for.\n";
        cin >> n;


        while (first <= last) {
            middle = first + last / 2;
            if (thisArray[middle] == n) {

                pos = middle;
                cout << "item found at " << middle + 1 << "\n";

                exit(0);
            }
            else if (thisArray[middle] > n) {
                last = middle - 1;
            }
            else {
                first = middle + 1;
            }//endif
        }//end while
    }//end big while
    //if()


    return 0;
}

我明白了。感谢大家的帮助！

Answer 1

由于和first == 0，它没有输出任何内容。因此last == -1永远不会成立，循环体永远不会被执行。

Answer 2

你知道吗？你怎么能使用二进制搜索如果数组没有正确排序使用二进制搜索属性...

请，请停止回答问题像杰克meagher风格，我讨厌回答不是＆＃39;直接解决这个问题，它有点重述了这个问题......

Answer 3

简单

将last = n - 1;更改为last = SIZE - 1;

或在您接受last = n - 1;

的值后计算n

此外，阵列需要排序！

Answer 4

想出来。现在虽然代码是一个例子，我发现for循环对我来说不正常，所以我摆脱它。对于迭代，我实现了一个do-while循环。但是，代码现在正常工作。

#include "stdafx.h"
#include <iostream>
#include <iomanip>
#include <conio.h>
#include <vector>
#include <algorithm>

using namespace std;
int SIZE = 10;

int main()
{
    //this is my binary search
    int thisArray[10] = { 0,11,32,44,55,63,78,86,99 };
    int i = 0; //index of the array
    int n = 0; //variable of number that will be looked for
    int first = 0;
    int last = SIZE - 1;
    int middle;
    int pos = -1;
    bool found = false;
    int count = 0;
    do {
        cout << "Enter a number to look for.\n";
        cin >> n;


        while (first <= last) {
            middle = first + last / 2;
            if (thisArray[middle] == n) {

                pos = middle;
                cout << "item found at " << middle + 1;
                exit(0);
            }
            else if (thisArray[middle] > n) {
                last = middle - 1;
            }
            else {
                first = middle + 1;
            }//endif
        }//end while
    } while (found = true);
    return 0;
}

二进制搜索 - 代码编译和运行后不显示输出

4 个答案: