一些常用的东西

整理一些常用的东西。

 

 1、cincout读入优化

 ios::sync_with_stdio(false);

2、“万能头文件”，别忘了命名空间

#include<bits/stdc++.h>
using namespace std;

等于

#include <iostream> 
#include <cstdio> 
#include <fstream> 
#include <algorithm> 
#include <cmath> 
#include <deque> 
#include <vector> 
#include <queue> 
#include <string> 
#include <cstring> 
#include <map> 
#include <stack> 
#include <set> 
using namespace std;

3、随机数函数

srand((unsigned)time(NULL));
n = rand(); 

srand和rand属于#include<algorithm>

time属于#include<ctime>

4、读入优化

int read()
{
    int x=0,f=1;char ch=getchar();
    while(ch<'0' || ch>'9'){if(ch=='-')f=-1;ch=getchar();}
    while(ch>='0'&& ch<='9'){x=x*10+ch-'0';ch=getchar();}
    return x*f;
}

fread的读入优化 

inline char nc() {
    static char buf[100000],*p1 = buf,*p2 = buf;
    return p1==p2&&(p2=(p1=buf)+fread(buf,1,100000,stdin),p1==p2) ? EOF :*p1++;
}
inline int read() {
    int x = 0,f = 1;char ch=nc();
    for (; ch<'0'||ch>'9'; ch = nc()) 
        if (ch == '-') f = -1;
    for (; ch>='0'&&ch<='9'; ch = nc()) 
        x = x*10+ch-'0';
    return x * f;
}

 带返回值的读入优化

inline char nc() {
    static char buf[100000],*p1 = buf,*p2 = buf;
    return p1==p2&&(p2=(p1=buf)+fread(buf,1,100000,stdin),p1==p2) ? EOF :*p1++;
}
inline bool read(int &x) {
    x = 0;
    int f = 1;char ch=nc();
    if (ch==EOF) return false;
    for (; ch<'0'||ch>'9'; ch = nc()) 
        if (ch == '-') f = -1;
    for (; ch>='0'&&ch<='9'; ch = nc()) 
        x = x*10+ch-'0';
    x = x * f;
    return true;
}

自己yy了一种读入优化，跑的飞快、、、

char buf[100000],*p1 = buf,*p2 = buf,ch;
#define nc() 
    p1==p2&&(p2=(p1=buf)+fread(buf,1,100000,stdin),p1==p2) ? EOF :*p1++;
#define read(x)  
    x=0;ch=nc(); 
    while(!isdigit(ch)) ch=nc();
    while(isdigit(ch))x=x*10+ch-'0',ch=nc();

char buf[100000],*_p1 = buf,*_p2 = buf;
#define nc() (_p1==_p2&&(_p2=(_p1=buf)+fread(buf,1,100000,stdin),_p1==_p2) ? EOF :*_p1++) 
inline int read() {
    int x=0,f=1;char ch=nc();for(;!isdigit(ch);ch=nc())if(ch=='-')f=-1;
    for (;isdigit(ch);ch=nc())x=x*10+ch-'0';return x*f;
}

小数读入优化

double read() {
    double x = 0, f = 1, y = 0.1; char ch = getchar();
    for (; !isdigit(ch)&&ch!='.'; ch=getchar()) if (ch=='-') f = -1;
    for (; isdigit(ch); ch=getchar()) x = x * 10 + ch - '0';
    if (ch == '.') ch = getchar();
    for (; isdigit(ch); ch=getchar()) x += (ch - '0') * y, y *= 0.1;
    return x * f;
}

5、c++STL堆定义

priority_queue<int>heap;//大根堆

priority_queue<int, vector<int>, greater<int> >heap;//小根堆

 小根堆

struct Node{
    int x,dis;
    bool operator < (const Node &a) const {
        return dis > a.dis;
    }
    Node() {}
    Node(int a,int b) {x = a,dis = b;}
};

大根堆

struct Node{
    int x,dis;
    bool operator < (const Node &a) const {
        return dis < a.dis;
    }
    Node() {}
    Node(int a,int b) {x = a,dis = b;}
};

6、Windows与Linux的long long类型的输入输出。

#ifdef WIN32
#define LL "%I64d"
#else
#define LL "%Ild"
#endif

7、结构体赋值，赋初值

快速赋值

struct Edge{
    int to,w,nxt;
    Edge(){}
    Edge(int x,int y,int z){to = x,w = y,nxt = z;}
}e[M];

 赋初值

struct Point {
    double x,y;
    Point() {x=1;y=2;} 
};

8、二进制统计0/1常用函数

__builtin_popcount(unsigned int n) 二进制下1个个数

__builtin_ffs(unsigned int n) 末尾最后一个1的位置

__builtin_ctz(unsigned int n) 末尾0的个数

__builtin_clz(unsigned int n) 前导0的个数

9、枚举子集

for (int i = s; i; i = (i - 1) &ｓ)

复杂度$3^n$

10、O(1)统计2^30一个数的二进制下1的个数。

int Calc(int x) {
    return num[x >> 15] + num[x & ((1 << 15) - 1)];
}
void init() {
    for (int i = 1; i < (1 << 13); ++i) num[i] = num[i >> 1] + (i & 1);
}

11、莫队的神奇排序方法

bool operator < (const Que &A,const Que &B) {
      return bel[A.l] < bel[B.l] || (bel[A.l] == bel[B.l] && ((bel[A.l] & 1) ? A.r < B.r : A.r > B.r));
}

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