数据结构实验5：查找

实验五：查找算法

实验目的
1.掌握顺序查找技术和拆半查找技术；
2. 掌握查找的算法实现

实验内容
1.产生n个随机整数用顺序查找的方法进行查找操作，要求输出要找关键字Key的过程。
1.给定n个有序整数用折半查找的方法进行查找操作，找关键字Key的过程。

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分析
签到级难度，主要是考察折半查找思想的理解和应用。折半查找又称二分查找，需要先对数组
进行排序。为了不打乱原来的数组，可以将排序后的数组另外保存，为了求出查到的数在原来的
数组所在的下标，可以用一个指针数组来排序和查找，得到的指针减去原数组的地址即可得到
所求树的位置。时间复杂度log2(n)。

MyCode

#include<iostream>
#include<stdio.h>
#include<string.h>
#include<string>
#include<algorithm>
#include<time.h>
using namespace std;
const int maxn = 20;		//size of randon integer
static int times = 1;		//used by printInt() to control the integer output each line 
int randArray[maxn];		//the array saving randon integer

//controal the format of print integer	
void  printInt(int n){		
	string blank = "              ";
	int len = 0;
	int tn = n;
	while (tn /= 10) len++;
	cout << n << blank.substr(0, 8-len);
	if (times % 10 == 0) cout << endl;
	times++;
}

void init(){
	srand(time(0));
	for (int i = 0; i < maxn; i++){
		randArray[i] = rand() % 1000000;
		printInt(randArray[i]);
	}
	cout << "\n\n";
}

//search a number by order
void seqSearchTest(){
	while (true){
		cout << "Please input the number you want to search, input -1 to exit \n";
		int input;
		int i = 0;
		cin >> input;
		if (input < 0) break;
		for (; i<maxn; i++){
			cout << randArray[i];
			if (randArray[i] == input) break;
			cout << "->";
		}
		if (randArray[i] == input){
			cout << "Find the integer you want, index is " << i << endl;
		}
		else{
			cout << i << " is not in the array!" << endl;
		}
	}
	return;
}

//define the way of sort the pointer array
bool cmp(int *&a, int *&b){
	return *a > *b;
}
//binary search the array and get the index 
void binSearchTest(){
	int *p[maxn];
	for (int i = 0; i < maxn; i++){
		p[i] = randArray + i;
	}
	sort(p, p + maxn, cmp);
	for (int i = 0; i < maxn; i++){
		printInt(*p[i]);
	}
	while (true){
		cout << "\nPlease input the number you want to search, input -1 to exit  > ";
		int input;
		int i = 0;
		cin >> input;
		if (input < 0) break;
		int lr = 0;
		int rr = maxn - 1;
		int mid;
		cout << "================ begin to search =================\n";
		while (lr <= rr){//##
			mid = (lr + rr) / 2;
			int midVal = *p[mid];
			cout << midVal;
			if (midVal == input){
				break;
			}
			cout << " -> ";
			if (midVal < input) 
				rr = mid - 1;
			else  
				lr = mid + 1;
		}
		cout << "\n===================================================\n";
		if (*p[mid] == input){
			cout << endl << "Find the integer you want , index is " << p[mid] - randArray << "\n\n";
		}
		else{
			cout << endl << "The integer you want not in the array ! \n\n";
		}
	}
	return;
}


int main(){
	init();
	//seqSearchTest();
	binSearchTest();
}

备忘录
binSearchTest() 中的循环条件 lr <= rr 非常容易出错，以后的代码设计中一定要针对类似的与数组边界的细节多
加谨慎。