solve: 07_reverse-integermain

i really enjoyed solving this one. mfw when i saw other's 0ms solution.

1 files changed, 44 insertions, 0 deletions

diff --git a/07_reverse-integer/src/main.rs b/07_reverse-integer/src/main.rs
new file mode 100644
index 0000000..2fb80c4
--- /dev/null
+++ b/07_reverse-integer/src/main.rs
@@ -0,0 +1,44 @@
+fn main() {
+    dbg!(Solution::reverse(1534236469));
+}
+
+struct Solution(());
+
+impl Solution {
+    pub fn reverse(x: i32) -> i32 {
+        let n = if x < 0 { x * -1 } else { x };
+
+        if let Some(i) = Self::invert(n as u32, 0).0 {
+            let t: u32 = 1 << 31;
+
+            if (i & t) == t {
+                return 0;
+            }
+
+            if x < 0 {
+                return i as i32 * -1;
+            }
+
+            return i as i32;
+        }
+
+        0
+    }
+
+    fn invert(n: u32, pow: u32) -> (Option<u32>, u32) {
+        if n < 10 {
+            return (Some(n), pow + 1);
+        }
+
+        let m = n % 10;
+        let d = (n - m) / 10;
+        let c = Self::invert(d, pow);
+
+        if let Some(inner) = c.0
+            && let Some(m) = m.checked_mul(10_u32.pow(c.1))
+        {
+            return (Some(m + inner), c.1 + 1);
+        }
+        (None, 0)
+    }
+}