Week 12

12.1 STL排序算法sort

STL概述

• STL: (Standard Template Library) 标准模板库
• 包含一些常用的算法如排序查找，还有常用的数据结构如可变长数组、链表 、字典等。
• 使用方便，效率较高
• 要使用其中的算法，需要#include <algorithm>

sort 排序

int a[] = {15,4,3,9,7,2,6};  sort(a,a+7); //对整个数组从小到大排序  
int a[] = {15,4,3,9,7,2,6};  sort(a,a+3); // 结果：{3,4,15,9,7,2,6} 
int a[] = {15,4,3,9,7,2,6};  sort(a+2,a+5); //结果：{15,4,3,7,9,2,6} 

从大到小

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
using namespace std;

struct Student {
	char Name[20];
	int ID;
	double GPA;
};

Student Students[]{
	{ "Jack",112,3.4 },{ "Mary",102,3.8 },{ "Mary",117,3.9 },{ "Ala",333,3.5 },{ "Zero",101,4.0 }
};

struct Rule1 {	 //按姓名从小到大排 
	bool operator()(const Student & s1, const Student & s2) {
		if (stricmp(s1.Name, s2.Name) < 0)
			return true;
		return false;
	}
};

struct Rule2 {	//按id从小到大排 
	bool operator()(const Student & s1, const Student & s2) {
		return s1.ID < s2.ID;
	}
};

struct Rule3 {	//按gpa从高到低排 
	bool operator()(const Student & s1, const Student & s2) {
		return s1.GPA > s2.GPA;
	}
};

void Print(Student s[], int size)
{
	for (int i = 0; i < size; ++i)
		cout << "(" << s[i].Name << "," << s[i].ID << "," << s[i].GPA << ")";
	cout << endl;
}

int main()
{
	int n = (sizeof(Students) / sizeof(Student));
	sort(Students, Students + n, Rule1());
	Print(Students, n);
	sort(Students, Students + n, Rule2());
	Print(Students, n);
	sort(Students, Students + n, Rule3());
	Print(Students, n);
	return 0;
}

12.2 STL二分查找算法

STL提供在排好序的数组上进行二分查找的算法

1. binary_search
2. lower_bound
3. upper_bound

binary_search

#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <algorithm>
using namespace std;

void Print(int a[], int size)
{
	for (int i = 0; i < size; ++i)
		cout << a[i] << ",";
	cout << endl;
}

struct Rule {
	bool operator()(const int & s1, const int & s2) {
		return s1 % 10 < s2 % 10;
	}
};

int main()
{
	int a[] = { 12,45,3,98,21,7,100 };
	sort(a, a + sizeof(a) / sizeof(int));
	Print(a, sizeof(a) / sizeof(int));
	cout << "result:" << binary_search(a, a + sizeof(a) / sizeof(int), 12) << endl;
	cout << "result:" << binary_search(a, a + sizeof(a) / sizeof(int), 77) << endl;
	sort(a, a + sizeof(a) / sizeof(int), Rule());
	Print(a, sizeof(a) / sizeof(int));
	cout << "result:" << binary_search(a, a + sizeof(a) / sizeof(int), 7) << endl;
	cout << "result:" << binary_search(a, a + sizeof(a) / sizeof(int), 8, Rule()) << endl;
	return 0;
}

倒数第二个result是0是因为没有给出查找规则，就默认按照从小到大的排列方式进行二分查找。
而最后一个result是1是因为按照Rule的规则，是按照个位数的大小排序，而8不是必须在98前面，也不是必须在98后面，所以8“等于”98。即：由于98和8的个位数都相同，程序认为他们“相等”，认为它能找到8，但是实际上找到的是98。

lower_bound

upper_bound

12.3 multiset

STL中的平衡二叉树数据结构

multiset

multiset用法实例

#include <iostream>
#include <cstdio>
#include <string>
#include <set>	//使用multiset和set需要此头文件 
using namespace std;

int main()
{
	multiset<int> st;
	int a[10] = { 1,14,12,13,7,13,21,19,8,8 };
	for (int i = 0; i < 10; ++i)
		st.insert(a[i]);	//插入的是a [i]的复制品 
	multiset<int>::iterator i;	//迭代器，近似于指针 
	for (i = st.begin(); i != st.end(); ++i)
		cout << *i << ",";
	cout << endl;
	i = st.find(22);	//查找22，返回值是迭代器 
	if (i == st.end())	 //找不到则返回值为 end() 
		cout << "NOT FOUND!" << endl;
	else
		cout << "FOUND:" << *i << endl;	//找到则返回指向找到的元素的迭代器
	i = st.insert(22);	 //插入 22 
	i = st.find(22);
	if (i == st.end())
		cout << "NOT FOUND!" << endl;
	else
		cout << "FOUND:" << *i << endl;
	for (i = st.begin(); i != st.end(); ++i)
		cout << *i << ",";
	cout << endl;
	i = st.lower_bound(13);
	cout << *i << endl;
	i = st.upper_bound(8);
	cout << *i << endl;
	st.erase(i);
	for (i = st.begin(); i != st.end(); ++i)
		cout << *i << ",";
	cout << endl;
	return 0;
}

12.4 自定义排序规则的multiset用法

#include <iostream>
#include <cstdio>
#include <cstring>
#include <set>
#include <functional>
using namespace std;

struct Rule {
//	bool operator()(const int & s1, const int & s2)const {
	bool operator()(const int & s1, const int & s2) {
		return (s1 % 10) < (s2 % 10);
	}
};

int main()
{
	multiset<int, greater<int>> st;
	int a[10] = { 1,14,12,13,7,13,21,19,8,8 };
	for (int i = 0; i < 10; ++i)
		st.insert(a[i]);
	multiset<int, greater<int>>::iterator i;
	for (i = st.begin(); i != st.end(); ++i)
		cout << *i << ",";
	cout << endl;
	i = st.find(133);
	if (i == st.end())
		cout << "NOT FOUND!" << endl;
	else
		cout << "FOUND:" << *i << endl;

	multiset<int, Rule> st2;
	for (int i = 0; i < 10; ++i)
		st2.insert(a[i]);
	multiset<int, Rule>::iterator p;
	for (p = st2.begin(); p != st2.end(); ++p)
		cout << *p << ",";
	cout << endl;
	p = st2.find(133);
	if (p == st2.end())
		cout << "NOT FOUND!" << endl;
	else
		cout << "FOUND:" << *p << endl;
	return 0;
}

我自己码的代码不知道为啥会报错，检查了好几遍没问题呀！复制了老师的代码也出错，好想在这里@他。。。

哈哈哈哈，上边的问题解决了！我是看了这篇文章之后有了点想法的其实，只要加一个const就好，心里路程那篇文章里有写。我认为最有用的一句话是

否则就会导致丢失const限定符的错误 因此解决办法就是给operator()加上const属性

12.5 set

#include <cstdio>
#include <cstring>
#include <set>
using namespace std;

int main()
{
	set<int> st;
	int a[10] = { 1,2,3,8,7,7,5,6,8,12 };
	for (int i = 0; i < 10; ++i)
		st.insert(a[i]);
	cout << st.size() << endl;
	set<int>::iterator i;
	for (i = st.begin(); i != st.end(); ++i)
		cout << *i << ",";
	cout << endl;
	pair<set<int>::iterator, bool> result = st.insert(2);
	if (!result.second)
		cout << *result.first << " already exists." << endl;
	else
		cout << *result.first << " inserted." << endl;
	return 0;
}