40 lines
850 B
Markdown
40 lines
850 B
Markdown
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### 快读快写
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```c++
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x << 1 == x * 2;
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x << 3 == x * 2 * 2 * 2;
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```
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二者相加也就是 `x * 10`;
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(1) 设$ch='3'$ $ASCII= 51 = 00110011(b)$
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(2) 字符 $'0'$ $ASCII= 48 = 00110000(b)$
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`^`运算规则：同$0$ 异$1$，相同的两个数异或为$0$ 不同的异或为$1$
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`ch^48` 相当于 `ch -= '0'` ，得到 $00000011$,即数字$3$
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```c++
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//快读
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inline int read() {
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int x = 0, f = 1;
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char ch = getchar();
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while (ch < '0' || ch > '9') {
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if (ch == '-') f = -1;
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ch = getchar();
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}
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while (ch >= '0' && ch <= '9') {
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x = (x << 3) + (x << 1) + (ch ^ 48);
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ch = getchar();
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}
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return x * f;
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}
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//快写
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inline void write(int x) {
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if (x < 0) putchar('-'), x = -x;
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if (x > 9) write(x / 10);
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putchar(x % 10 + '0');
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}
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```
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