二分查找

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本文深入探讨了二分查找算法的实现，展示了如何在有序序列中查找特定元素，并提供了详细的C++代码示例，包括主函数和打印结果的完整流程。

1. 二分查找

输入是有序的序列。待查找元素如果存在，输出索引，如果不存在，输出-1.

//
//  main.cpp
//  algorithm
//
//  Created by ybwang on 2019/11/5.
//  Copyright © 2019 ybwang. All rights reserved.
//

#include <iostream>

//二分查找
template <typename T>
int binarySearch(T* arr, int size, const T &key){
    int left = 0;
    int right = size - 1;
    int middle;
    while(left <= right){
        middle = (left + right) / 2;
        if(arr[middle] == key){
            return middle;
        }else if(arr[middle] < key){//小了，在右边，更新左边界
            left = middle + 1;
        }else{
            right = middle - 1;
        }
    }
    return -1;
}

void print(int* arr, int size, int value){
    int ret = binarySearch(arr, size, value);
    if(ret == -1){
        std::cout << value << " is not in" << std::endl;
    }else{
        std::cout << value << " position is " << ret << std::endl;;
    }
    
}

int main(int argc, const char * argv[]) {
    // insert code here...
    int a[13] = {1,2,3,4,5,6,7,8,9,10,15,27,31};
    print(a, 13, 0);
    for (int i=0; i<13; i++) {
        print(a, 13, a[i]);
    }
    print(a, 13, 32);
    return 0;
}

0 is not in
1 position is 0
2 position is 1
3 position is 2
4 position is 3
5 position is 4
6 position is 5
7 position is 6
8 position is 7
9 position is 8
10 position is 9
15 position is 10
27 position is 11
31 position is 12
32 is not in
Program ended with exit code: 0