Binary Search 二分查找,二分搜索 C++
// BSearch.cpp : Defines the entry point for the console application.
//
#include "stdafx.h"
#include <iostream>
using namespace std;
template <class T>
void PrintfNum(T a[],const int& n);
/**
* search n in a[], return the index, if not find, return -1.
*/
template <class T>
int BSearch(T a[],const int& length,const int& n){
int left = 0, right = length - 1;
while(left <= right){
int middle = (left + right) / 2;
//cout << "middle:" <<middle << " ,left:" << left << " ,right:" << right << endl;
if(n < a[middle]){
right = middle - 1;
}else if(n > a[middle]){
left = middle + 1;
}else{
return middle;
}
}
return -1;
}
/**
* A better one
* search n in a[], return the index, if not find, return -1.
*/
template <class T>
int BetterBSearch(T a[],const int& length,const int& n){
int left = -1, right = length - 1;
while(left+1 != right){ //left < right && a[left] < n <= a[right]
int middle = (left + right) / 2;
if(a[middle] < n){ //a[left] < n
left = middle;
}else{ //a[right] >= n
right = middle;
}
}
if(right >= length || a[right] != n )//no find
return - 1;
return right;
}
/**
* Test function
*/
bool TestBSearch(){
const int NUM = 20;
int BeginNum = 10;
int t[NUM];
for(int i = 0; i< NUM; ++i){
t[i] = BeginNum;
++BeginNum;
}
bool result = true;
for(int j = 0 ;j < NUM; ++j){
if(BSearch(t, NUM , t[j]) != j){
result = false;
}
}
// test no find
if(BSearch(t,NUM,t[0] - 1) != -1 || BSearch(t,NUM,t[NUM-1] + 1) != -1){
result = false;
}
return result;
}
/**
* Test function
*/
bool TestBetterBSearch(){
const int NUM = 20;
int BeginNum = 10;
int t[NUM];
for(int i = 0; i< NUM; ++i){
t[i] = BeginNum;
++BeginNum;
}
bool result = true;
for(int j = 0 ;j < NUM; ++j){
if(BetterBSearch(t, NUM , t[j]) != j){
result = false;
}
}
// test no find
if(BetterBSearch(t,NUM,t[0] - 1) != -1 || BetterBSearch(t,NUM,t[NUM-1] + 1) != -1){
result = false;
}
return result;
}
int main(int argc, char* argv[])
{
const int NUM = 10;
int t[NUM] = {10,11,12,13,14,15,16,17,18,20};
PrintfNum(t,NUM);
for(int i = 0 ;i < NUM; ++i){
cout << t[i] << " was at index: " << BSearch(t, NUM , t[i]) << endl;
}
cout << "searching 100 in array t, result: "<< BSearch(t, NUM , 100) << endl;
cout << endl;
cout << "BSearch test result:" << TestBSearch() << endl;
cout << "BetterBSearch test result:" << TestBetterBSearch() << endl;
return 0;
}
template <class T>
void PrintfNum(T a[],const int& n){
for(int i = 0; i < n; ++i){
cout << a[i] << ",";
}
cout << endl;
}
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