Improved p29 solution

src/p29_divide_two_integers.rs

@@ -1,11 +1,6 @@
 pub struct Solution;
 impl Solution {
-    // terrible solutionE
-    // should use approximation using shifts
     pub fn divide(mut dividend: i32, mut divisor: i32) -> i32 {
-        if dividend == i32::MAX && divisor == i32::MIN {
-            return 0;
-        }
         if divisor == 1 {
             return dividend;
         }
@@ -15,25 +10,34 @@ impl Solution {
             }
             return -dividend;
         }
-        let mut result = 0;
+        if divisor == dividend {
-        let is_neg = (dividend < 0) ^ (divisor < 0);
+            return 1;
-        let mut one = false;
-        dividend = if dividend == i32::MIN {
-            one = true;
-            i32::MAX
-        } else { dividend.abs() };
-        divisor = if divisor == i32::MIN { i32::MAX } else { divisor.abs() };
-        while dividend >= divisor {
-            dividend -= divisor;
-            result += 1;
         }
-        if one && dividend - divisor == -1 {
+        let (mut is_pos, mut quotient) = (true, 0); 
-            result += 1;
+        if dividend >= 0 {
+            dividend = -dividend;
+            is_pos = !is_pos;
         }
-        if is_neg {
+        if divisor >= 0 {
-            result = -result;
+            divisor = -divisor;
+            is_pos = !is_pos;
         }
-        return result;
+        while dividend <= divisor {
+            let mut shift = 0;
+            loop {
+                let shifted = divisor << (shift + 1);
+                if shifted <= dividend || shifted > 0 {
+                    break;
+                }
+                shift += 1;
+            }
+            quotient -= 1 << shift;
+            dividend -= divisor << shift;
+        }
+        if is_pos {
+            quotient = -quotient;
+        }
+        return quotient;
     }
 }
 
@@ -60,4 +64,9 @@ mod tests {
     fn test4() {
         assert_eq!(Solution::divide(-2147483648, -1), 2147483647);
     }
+
+    #[test]
+    fn test5() {
+        assert_eq!(Solution::divide(-2147483648, 3), -715827882);
+    }
 }