卡常技巧

swap

a^=b^=a^=b;//without function
<=
inline void swap(int &x,int &b){
  a^=b^=a^=b;
}
<=
swap(a,b);//stl

究极快读

namespace fast_IO {//without negative number
    char getchar() {
        static const int IN_LEN = 1 << 18 | 1;
        static char buf[IN_LEN], *s, *t;
        return (s == t) && (t = (s = buf) + fread(buf, 1, IN_LEN, stdin)), s == t ? -1 : *s++;
    }
    int read() {
        int num = 0;
        char c;
        while ((c = getchar()) != '-' && c != '+' && (c < '0' || c > '9') && ~c);
        num = c ^ 48;
        while ((c = getchar()) >= '0' && c <= '9')
            num = (num << 1) + (num << 3) + (c ^ 48);
        return num;
    }
}
namespace fast_IO {
    char buf[N], *s, *t;
    char getchar() {
        return (s == t) && (t = (s = buf) + fread(buf, 1, N, stdin)), s == t ? -1 : *s++;
    }
    int read() {
        int num = 0;
        char c;
        bool tag = false;
        while ((c = getchar()) != '-' && c != '+' && (c < '0' || c > '9') && ~c);
        if (c == '-')tag = true;
        else num = c ^ 48;
        while ((c = getchar()) >= '0' && c <= '9')
            num = (num << 1) + (num << 3) + (c ^ 48);
        if (tag)return -num;
        return num;
    }
}

GCD

inline int gcd(int a,int b){if(!b)return a;while(b^=a^=b^=a%=b);return a;

氧气加速

#pragma GCC optimize(2)
#pragma GCC optimize(3,"Ofast","inline")