init commit

archive/algorithm/leetcode/29.c

@@ -0,0 +1,127 @@
+#include <stdio.h>
+
+/**
+ * https://leetcode-cn.com/problems/divide-two-integers/description/
+ * 两数相除,不能直接使用乘法除法
+ */
+
+int add(int num1, int num2)
+{
+    while (num2)
+    {
+        int tmp = num1 ^ num2;
+        num2 = (num1 & num2) << 1;
+        num1 = tmp;
+    }
+    return num1;
+}
+int sub(int num1, int num2)
+{
+    return add(num1, add(~num2, 1));
+}
+
+int negative(int num) //判断负数
+{
+    return (num >> 31) & 1;
+}
+
+int abs_(int num)
+{
+    if (negative(num)) //右移31位判断正负
+    {
+        return add(~num, 1); //负数
+    }
+    return num;
+}
+
+int divide(int dividend, int divisor)
+{
+    int flag = 1;
+    if (negative(dividend) == negative(divisor))
+    {
+        flag = 0;
+    }
+    unsigned int x = abs_(dividend);
+    unsigned int y = abs_(divisor);
+    unsigned int result = 0;
+    for (int i = 31; i >= 0; i--)
+    {
+        if ((x >> i) >= y)
+        {
+            result = add(result, 1 << i);
+            x = sub(x, y << i);
+        }
+    }
+    if (flag)
+    {
+        //负数
+        if (result > 2147483648)
+        {
+            return 2147483647;
+        }
+        return add(~result,1);
+    }
+    else
+    {
+        //正数
+        if (result > 2147483647)
+        {
+            return 2147483647;
+        }
+        return result;
+    }
+}
+
+/*
+    对于int a = 0x80000000;
+        long long int b = -a;
+        而言，b依然是-2147483648，只不过是长长整型的-2147483648
+        可能是右边的-a运算，由于预期的结果溢出，所以就没有做负号运算
+        原先认为的是-a会导致溢出从而结果为0，实际测试发现不是
+    long long int d = ((long long int)dividend > 0) ? (long long int)dividend : -(long long int)dividend;
+    long long int div = ((long long int)divisor > 0) ? (long long int)divisor : -(long long int)divisor;
+*/
+/**
+int divide(int dividend, int divisor) {
+    if (divisor == 1)
+        return dividend;
+    
+    if (divisor == -1)
+    {
+        if (dividend == (int)0x80000000)
+            return 0x7FFFFFFF;
+        else
+            return -dividend;
+    }
+    
+    int cnt = 0, factor = 0, i = 0;
+    long long int d = dividend;
+    long long int div = divisor;
+    
+    d = (d > 0) ? d : -d;
+    div = (div > 0) ? div : -div;
+    
+    if ((dividend ^ divisor) & 0x80000000)
+        factor = -1;
+    else
+        factor = 1;
+    
+    while (d >= div)
+    {
+        i = 0;
+        while (d >= (div << i))
+        {
+            d -= (div << i);
+            cnt += (1 << i++);
+        }
+    }
+    
+    return factor*cnt;
+}
+*/
+int main()
+{
+    printf("%d\n", divide(-2147483648, -1));
+    getchar();
+    return 0;
+}