X times 7 | tech::interview
x * 7 = x * 4 + x * 2 + x
= (x << 2) + (x << 1) + x
= add(x << 2, add(x << 1, x))
所以本质上这题就是考用二进制实现add函数。
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Write a function to calculate x * 7 without using + - / * %.x * 7可以做如下分解：
x * 7 = x * 4 + x * 2 + x
= (x << 2) + (x << 1) + x
= add(x << 2, add(x << 1, x))
所以本质上这题就是考用二进制实现add函数。
int add(int a, int b) {int sum, carry;do {sum = a ^ b;carry = (a & b) << 1;a = sum;b = carry;} while (b);return a;}int times_7(int val) {return add(val << 2, add(val << 1, val));}
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