以下内容大部分使用 C++11 !
以下内容大部分使用 C++11 !
以下内容大部分使用 C++11 !
通过 {} 来给容器赋值
pair<int, int> p;
// ...
p = make_pair(3, 4);
其实可以这样
pair<int, int> p;
// ...
p = {3, 4};
对于复杂的 pair
pair<int, pair<char, long long> > p;
// ...
p = {3, {'a', 8ll}};
对于其他容器(vector,deque,set)
vector<int> v;
v = {1, 2, 5, 2};
for (auto i: v)
cout << i << ' ';
cout << '
';
// prints "1 2 5 2"
deque<vector<pair<int, int>>> d;
d = {{{3, 4}, {5, 6}}, {{1, 2}, {3, 4}}};
for (auto i: d) {
for (auto j: i)
cout << j.first << ' ' << j.second << '
';
cout << "-
";
}
// prints "3 4
// 5 6
// -
// 1 2
// 3 4
// -"
set<int> s;
s = {4, 6, 2, 7, 4};
for (auto i: s)
cout << i << ' ';
cout << '
';
// prints "2 4 6 7"
list<int> l;
l = {5, 6, 9, 1};
for (auto i: l)
cout << i << ' ';
cout << '
';
// prints "5 6 9 1"
array<int, 4> a;
a = {5, 8, 9, 2};
for (auto i: a)
cout << i << ' ';
cout << '
';
// prints "5 8 9 2"
tuple<int, int, char> t;
t = {3, 4, 'f'};
cout << get<2>(t) << '
';
注意：stack,queue不适用
宏
通过 '#' 来得到参数名
#define what_is(x) cerr << #x << " is " << x << endl;
// ...
int a_variable = 376;
what_is(a_variable);
// prints "a_variable is 376"
what_is(a_variable * 2 + 1)
// prints "a_variable * 2 + 1 is 753"
使用 <bits/stdc++.h>
#include <bits/stdc++.h>
库中自带却不怎么常用的函数
- __gcd(value1,value2)
e.g. __gcd(18, 27) = 9. - __builtin_ffs(x)
e.g. __builtin_ffs(10) = 2 because 10 is '...10 1 0' in base 2 and first 1-bit from right is at index 1 (0-based) ’and function returns 1 + index. - __builtin_clz(x)
e.g. __builtin_clz(16) = 27 because 16 is ' ... 10000'. Number of bits in a unsigned int is 32. so function returns 32 — 5 = 27. - __builtin_ctz(x)
e.g. __builtin_ctz(16) = 4 because 16 is '...1 0000 '. Number of trailing 0-bits is 4. - __builtin_popcount(x)
e.g. __builtin_popcount(14) = 3 because 14 is '... 111 0' and has three 1-bits.
Note 还有其他 __bultin 函数,但是不怎么常用,cpp
变长参数函数与宏
int sum() { return 0; }
template<typename... Args>
int sum(int a, Args... args) { return a + sum(args...); }
int main() { cout << sum(5, 7, 2, 2) + sum(3, 4); /* prints "23" */ }
不止是 int
int sum() { return 0; }
template<typename T, typename... Args>
T sum(T a, Args... args) { return a + sum(args...); }
int main() { cout << sum(5, 7, 2, 2) + sum(3.14, 4.89); /* prints "24.03" */ }
C++14 可以用 auto sum(T a, Args... args)
使用宏
#define a_macro(args...) sum(args...)
int sum() { return 0; }
template<typename T, typename... Args>
auto sum(T a, Args... args) { return a + sum(args...); }
int main() { cout << a_macro(5, 7, 2, 2) + a_macro(3.14, 4.89); /* prints "24.03" */ }
=> debug 函数
#include <bits/stdc++.h>
using namespace std;
#define error(args...) { vector<string> _v = split(#args, ','); err(_v.begin(), args); }
vector<string> split(const string& s, char c) {
vector<string> v;
stringstream ss(s);
string x;
while (getline(ss, x, c))
v.emplace_back(x);
return move(v);
}
void err(vector<string>::iterator it) {}
template<typename T, typename... Args>
void err(vector<string>::iterator it, T a, Args... args) {
cerr << it -> substr((*it)[0] == ' ', it -> length()) << " = " << a << '
';
err(++it, args...);
}
int main() {
int a = 4, b = 8, c = 9;
error(a, b, c);
}
/*
Output:
a = 4
b = 8
c = 9
*/
C++0x 与 C++
遍历
set<int> s = {8, 2, 3, 1};
for (set<int>::iterator it = s.begin(); it != s.end(); ++it)
cout << *it << ' ';
// prints "1 2 3 8"
上面代码好长呀,可以这样
set<int> s = {8, 2, 3, 1};
for (auto it: s)
cout << it << ' ';
// prints "1 2 3 8"
可以用 &auto 来 替代 auto
vector<int> v = {8, 2, 3, 1};
for (auto &it: v) it *= 2;
for (auto it: v) cout << it << ' ';
// prints "16 4 6 2"
Power of auto
set<pair<int, pair<int, int> > >::iterator
可以这样写 auto it = s.begin()
for(i = 1; i <= n; i++) {
for(j = 1; j <= m; j++)
cout << a[i][j] << " ";
cout << "
";
}
等价于
for(i = 1; i <= n; i++)
for(j = 1; j <= m; j++)
cout << a[i][j] << "
"[j == m];
tie 和 emplace_back
#define mt make_tuple
#define eb emplace_back
typedef tuple<int,int,int> State; // operator< defined
int main(){
int a,b,c;
tie(a,b,c) = mt(1,2,3); // assign
tie(a,b) = mt(b,a); // swap(a,b)
vector<pair<int,int>> v;
v.eb(a,b); // shorter and faster than pb(mp(a,b))
// Dijkstra
priority_queue<State> q;
q.emplace(0,src,-1);
while(q.size()){
int dist, node, prev;
tie(dist, ode, prev) = q.top(); q.pop();
dist = -dist;
// ~~ find next state ~~
q.emplace(-new_dist, new_node, node);
}
}
emplace_back 比 push_back更快，紧跟末尾比在他处快？
tie 中可以使用 ignore 来忽略值
tuple<int, int, int, char> t (3, 4, 5, 'g');
int a, b;
tie(b, ignore, a, ignore) = t;
cout << a << ' ' << b << '
';
/*
Output:
5 3
*/
利用宏来循环
#define rep(i, begin, end) for (__typeof(end) i = (begin) - ((begin) > (end)); i != (end) - ((begin) > (end)); i += 1 - 2 * ((begin) > (end)))
- 不需要指明类型
- 从 begin 到 end
vector<int> v = {4, 5, 6, 4, 8};
rep(it, end(v), begin(v))
cout << *it << ' ';
// prints "8 4 6 5 4"
lambda function
[capture list](parameters) -> return value { body }
e.g.
auto f = [] (int a, int b) -> int { return a + b; };
cout << f(1, 2); // prints "3"
可以在 for_each,sort等 STL 中使用
vector<int> v = {3, 1, 2, 1, 8};
sort(begin(v), end(v), [] (int a, int b) { return a > b; });
for (auto i: v) cout << i << ' ';
/*
Output:
8 3 2 1 1
*/
move 的用法
使用move 来移动容器，不需要 copy
vector<int> v = {1, 2, 3, 4};
vector<int> w = move(v);
cout << "v: ";
for (auto i: v)
cout << i << ' ';
cout << "
w: ";
for (auto i: w)
cout << i << ' ';
/*
Output:
v:
w: 1 2 3 4
*/
C++0x Strings
Raw Strings
string s = R"(Hello, World!)"; // Stored: "Hello, World!"
A raw string skips all escape characters like
or ". e.g.
string str = "Hello World
";
string r_str = R"(Hello World
)";
cout << str << r_str;
/*
Output:
Hello World
Hello World
*/
// You can also have multiple line raw string:
string r_str =
R"(Dear Programmers,
I'm using C++11
Regards, Swift!)";
cout << r_str;
/*
Output:
Dear Programmer,
I'm using C++11
Regards, Swift!
*/
Regular Expressions (regex)
** e.g.** regex r = "[a-z]+";
regex email_pattern(R"(^[a-zA-Z0-9_.+-]+@[a-zA-Z0-9-]+.[a-zA-Z0-9-.]+$)");
// This email pattern is not totally correct! It's correct for most emails.
string
valid_email("swift@codeforces.com"),
invalid_email("hello world");
if (regex_match(valid_email, email_pattern))
cout << valid_email << " is valid
";
else
cout << valid_email << " is invalid
";
if (regex_match(invalid_email, email_pattern))
cout << invalid_email << " is valid
";
else
cout << invalid_email << " is invalid
";
/*
Output:
swift@codeforces.com is valid
hello world is invalid
*/
户定义数据标识 (User-defined literals)
栗子 0xA,1000ll,3.14f等等
long long operator "" _m(unsigned long long literal) {
return literal;
}
long double operator "" _cm(unsigned long long literal) {
return literal / 100.0;
}
long long operator "" _km(unsigned long long literal) {
return literal * 1000;
}
int main() {
// See results in meter:
cout << 250_m << " meters
"; // Prints 250 meters
cout << 12_km << " meters
"; // Prints 12000 meters
cout << 421_cm << " meters
"; // Prints 4.21 meters
}
Note 需要添加下划线_
声明如下
[returnType] operator "" _[name]([parameters]) { [body] }
Note 参数仅能使用如下
(const char *)
(unsigned long long int)
(long double)
(char)
(wchar_t)
(char16_t)
(char32_t)
(const char *, size_t)
(const wchar_t *, size_t)
(const char16_t *, size_t)
(const char32_t *, size_t)
原贴
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