python/TangDou/CSP-J/J2-2021/快读快写.md

快读快写

x << 1 == x * 2; 
x << 3 == x * 2 * 2 * 2;

二者相加也就是 x * 10;

(1) 设ch='3' ASCII= 51 = 00110011(b) (2) 字符 '0' 　ASCII= 48 = 00110000(b)

^运算规则：同0 异$1$，相同的两个数异或为0 不同的异或为1

ch^48 相当于 ch -= '0' ，得到 00000011,即数字3

//快读
inline 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 << 3) + (x << 1) + (ch ^ 48);
        ch = getchar();
    }
    return x * f;
}

//快写
inline void write(int x) {
    if (x < 0) putchar('-'), x = -x;
    if (x > 9) write(x / 10);
    putchar(x % 10 + '0');
}