1.泛型算法:
大多数算法定义在头文件algorithm中,标准库还在头文件numeric中定义了一组数值泛型算法
只读算法:
举例:
find函数用于找出容器中一个特定的值,有三个参数
int val = 10;//val为我们需要查找的值 auto result = find(vec.begin(), vec.end(), val): cout << "The value "<< val << (result == vec.end() ? "is not present" : "is present") << endl;
count函数用来统计容器中元素个数,下面给出例子:
#include <iostream> #include <deque> #include <algorithm> using namespace std; int main() { string val("hello"); deque<string> str; for(int i = 0; i<10; i++) { str.push_front(string("hello")); } int num = count(str.begin(), str.end(), val); cout << "The "<< "hello" << " num is: " << num << endl; return 0; }可以正确的统计出个数为10;
accumulate函数定义在numeric头文件中,用于统计指定迭代器范围内元素的和。
第三个参数是和的初值,用一般为0.
int num = accumulate(vec.begin(), vec.end(), 0);
#include <iostream> #include <deque> #include <vector> #include <algorithm> #include <numeric> using namespace std; int main() { string val("hello"); deque<string> str; vector<int> v; for(int i = 0; i<10; i++) { str.push_front(string("hello")); v.push_back(i); } int num = count(str.begin(), str.end(), val); string s = accumulate(str.begin(), str.end(), string("")); int sum = accumulate(v.begin(), v.end(), 0); cout << "sum of v: " << sum << endl; cout << "sum of str: " << s << endl; cout << "The "<< "hello" << " num is: " << num << endl; return 0; }运行结果:
sum of v: 45
sum of str: hellohellohellohellohellohellohellohellohellohello
The hello num is: 10
写容器元素算法:
fill函数用来向给定范围内容器写入数据。
fill(v.begin(), v.end(), 0); //将每个元素置为0
fill_n函数用来向指定位置写入指定个数的元素值。
fill_n(v.begin(), v.size(), 0); //将所有元素置为0
注意:不要在空容器上调用fill_n(或其他类似的写元素算法)
vector<int> v; //空容器 fill_n(v.begin(), 10, 0); //灾难!修改v中不存在的10个元素值
#include <iostream> #include <deque> #include <vector> #include <algorithm> #include <numeric> using namespace std; int main() { string val("hello"); deque<string> str; vector<int> v; for(int i = 0; i<10; i++) { str.push_front(string("hello")); v.push_back(i); } int num = count(str.begin(), str.end(), val); string s = accumulate(str.begin(), str.end(), string("")); int sum = accumulate(v.begin(), v.end(), 0); cout << "sum of v: " << sum << endl; cout << "sum of str: " << s << endl; cout << "The "<< "hello" << " num is: " << num << endl; // fill(v.begin(), v.end(), 0);//fill 0 fill_n(v.begin()+2, v.size()-3, 0);//0、1、2... 从2开始删除保留9 for(vector<int>::iterator i = v.begin(); i!=v.end(); ++i) { cout << *i << " "; } cout << endl; vector<int> vv;//空容器 //fill_n(vv.begin(), 10, 0); segment fault! 会产生段错误! return 0; }
int a1[] = {0, 1, 2, 3, 4, 5, 6, 7, 8, 9}; int a2[sizeof(a1) / sizeof(a1[0])];//a2与a1一样大 copy(begin(a1), end(a1), a2);//把a1内容拷贝到a2
sort函数&unique函数:
sort函数接受两个迭代器,表示要排序的元素范围。它会使不重复的元素出现在vector的头部。最后面则是重复的元素
我们希望相邻的重复元素只保留一个,可以与unique函数配合使用,unique返回迭代器指向最后一个不重复元素之后的位置。
假设初识序列如下:
[the quick red fox jumps over the slow red turtle]
sort排序后:
[fox jumps over quick red red slow the the turtle]
使用unique后:
[fox jumps over quick red slow the turtle the turtle]
容器本身的大小并没有改变。
由于unique函数返回的是指向最后一个不重复元素之后的位置的迭代器
所以我们可以将最后的重复元素用erase删除。
words.erase(end_unique, words.end());
最终得到:[fox jumps over quick red slow the turtle]
完整的程序如下:
#include <iostream> #include <vector> #include <algorithm> using namespace std; void elimDups(vector<string> &words) { sort(words.begin(), words.end()); vector<string>::iterator i = unique(words.begin(), words.end()); words.erase(i, words.end()); return ; } void print(vector<string> &vec) { for(vector<string>::iterator i = vec.begin(); i!=vec.end(); ++i) { cout << *i << " "; } cout << endl; } int main() { string s[] = {"the", "quick", "red", "fox", "jumps", "over", "the", "slow", "red", "turtle"}; vector<string> vec(s, s+sizeof(s)/sizeof(s[0])); print(vec); elimDups(vec); cout << "---------------------------------------------" << endl; print(vec); return 0; }
the quick red fox jumps over the slow red turtle
---------------------------------------------
fox jumps over quick red slow the turtle
C++ Primer笔记6_STL之泛型算法,布布扣,bubuko.com
原文地址:http://blog.csdn.net/scottly1/article/details/28619089