二分搜索算法

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二分搜索算法是计算机程序设计中的基础算法，1946年第一篇二分搜索算法的论文发表，第一个正确的算法实现是在1962年，中间相隔16年，这一事实令人深思。据了解训练有素的程序员仅有10%的人能够在数小时内写出完全正确的代码实现。因此，我也进行了尝试。现将实现如下贴出，不能保证完全正确，欢迎批评指正。

BinarySearch.h

#ifndef BinarySearch_H#define BinarySearch_H#include <assert.h>template<class T>T *binarySearch(T value,T a[],int left,int right,int *index){    assert(a);    if (left > right)    {        *index = -1;        return NULL;    }    int mid = (right + left)/2;    if (value == a[mid])    {        *index = mid;        return &a[mid];    }    else if (value < a[mid])    {        return binarySearch(value,a,left,mid-1,index);    }    else if (value > a[mid])    {        return binarySearch(value,a,mid+1,right,index);    }}template<class T>T *binSearch(T value,T a[],int n,int *index){    assert(a);    int left = 0;    int right = n-1;    int mid;    while (left <= right)    {        mid = (left+right)/2;        if (a[mid] == value)        {            *index = mid;            return &a[mid];        }        else if (a[mid] > value)        {            right = mid - 1;        }        else        {            left = mid + 1;        }    }    *index = -1;    return NULL;}#endif

main.cc

using namespace std;template <class T>void output(T a[],int n);int main(){    int a[] = {-5,-3,0,0,2,2,2,2,6,8};    int n = sizeof(a)/sizeof(a[0]);    cout << "The a[] ";    output(a,n);    int index;    int test[] = {-6,-5,-3,0,0,1,2,2,2,2,6,8,9};    int len = sizeof(test)/sizeof(test[0]);    int i;    cout << "The test[] ";    output(test,len);    cout << "递归二分搜索算法" <<endl;    for (i = 0;i < len;i++)    {        if (binarySearch(test[i],a,0,n-1,&index)==NULL)        {            cout << test[i] << " The index is null" << endl;            continue;        }        cout << *binarySearch(test[i],a,0,len-1,&index) << " ";        cout <<"The index is:"<< index << endl;    }    cout << "循环二分搜索算法" <<endl;    for (i = 0;i < len;i++)    {        if (binSearch(test[i],a,n,&index)==NULL)        {            cout << test[i] << " The index is null" << endl;            continue;        }        cout << *binSearch(test[i],a,len,&index) << " ";        cout <<"The index is:"<< index << endl;    }    return 0;}template <class T>void output(T a[],int n){    assert(a);    int i = 0;    for (; i < n; i++)        cout << a[i] <<" ";    cout << endl;}

makefile

main:main.o        g++ -o main main.omain.o:main.cc BinarySearch.h        g++ -c main.ccclean:        rm -f main *.o *.s *.i *.gch

执行 make命令，./main结果

root@duyuqi-OptiPlex-380:~/DataStruct/Algorithms/search# makeg++ -c main.ccg++ -o main main.oroot@duyuqi-OptiPlex-380:~/DataStruct/Algorithms/search# ./mainThe a[] -5 -3 0 0 2 2 2 2 6 8 The test[] -6 -5 -3 0 0 1 2 2 2 2 6 8 9 递归二分搜索算法-6 The index is null-5 The index is:0-3 The index is:10 The index is:20 The index is:21 The index is null2 The index is:62 The index is:62 The index is:62 The index is:66 The index is:88 The index is:99 The index is null循环二分搜索算法-6 The index is null-5 The index is:0-3 The index is:10 The index is:20 The index is:21 The index is null2 The index is:62 The index is:62 The index is:62 The index is:66 The index is:88 The index is:99 The index is null