《Cracking the Coding Interview》——第7章：数学和概率论——题目4

2014-03-20 02:16

题目：只用加法和赋值，实现减法、乘法、除法。

解法：我只实现了整数范围内的。减法就是加上相反数。乘法就是连着加上很多个。除法就是减到不能减为止，数数总共减了多少个。

代码：

 // 7.4 Implement the -*/ function with only the + operator.
 // You cannot use bit operation, although you might want it for efficiency.
 #include <cstdio>
 using namespace std;

 int negate(int n)
 {
     int one = (n >=  ? - : );
     int res = ;

     while (n != ) {
         n += one;
         res += one;
     }

     return res;
 }

 int add(int x, int y)
 {
     return x + y;
 }

 int subtract(int x, int y)
 {
     return x + negate(y);
 }

 int multiply(int x, int y)
 {
     int res = ;
     int value = (x >=  ? y : negate(y));
     int one = (x >=  ? - : );

     while (x != ) {
         res += value;
         x += one;
     }

     return res;
 }

 int divide(int x, int y)
 {
     if (y == ) {
         return ;
     }
     if (x == ) {
         return ;
     }

     int res = ;
     int one = ;
     int negone = -;
     int negy = negate(y);

     if (x > ) {
         if (y > ) {
             while (x >= y) {
                 x += negy;
                 res += one;
             }
         } else {
             while (x >= negy) {
                 x += y;
                 res += negone;
             }
         }
     } else {
         if (y > ) {
             while (x <= negy) {
                 x += y;
                 res += negone;
             }
         } else {
             while (x <= y) {
                 x += negy;
                 res += one;
             }
         }
     }

     return res;
 }

 int main()
 {
     char s[];
     int a, b;
     int res;

     while (scanf("%d%s%d", &a, s, &b) == ) {
         switch (s[]) {
         case '+':
             res = add(a, b);
             break;
         case '-':
             res = subtract(a, b);
             break;
         case '*':
             res = multiply(a, b);
             break;
         case '/':
             res = divide(a, b);
             break;
         }
         printf("%d\n", res);
     }

     return ;
 }