add power_of_four (#20)

Author: 0xmountaintop

README.md

@@ -64,10 +64,10 @@ cargo test
 0260 | [Single Number III](https://leetcode.com/problems/single-number-iii/) | [C++](https://github.com/kamyu104/LeetCode-Solutions/blob/master/C++/single-number-iii.cpp) [Python](https://github.com/kamyu104/LeetCode-Solutions/blob/master/Python/single-number-iii.py) <br>------</br> [Rust](./kamyu104/src/single_number_iii.rs) | _O(n)_ | _O(1)_          | Medium         ||
 0268| [Missing Number](https://leetcode.com/problems/missing-number/) | [C++](https://github.com/kamyu104/LeetCode-Solutions/blob/master/C++/missing-number.cpp) [Python](https://github.com/kamyu104/LeetCode-Solutions/blob/master/Python/missing-number.py) <br>------</br> [Rust](./kamyu104/src/missing_number.rs) | _O(n)_ |  _O(1)_ | Medium         | LintCode ||
 0318| [Maximum Product of Word Lengths](https://leetcode.com/problems/maximum-product-of-word-lengths/) | [C++](https://github.com/kamyu104/LeetCode-Solutions/blob/master/C++/maximum-product-of-word-lengths.cpp) [Python](https://github.com/kamyu104/LeetCode-Solutions/blob/master/Python/maximum-product-of-word-lengths.py) <br>------</br> [Rust](./kamyu104/src/maximum_product_of_word_lengths.rs) | _O(n)_ ~ _O(n^2)_ |  _O(n)_ | Medium         || Bit Manipulation, Counting Sort, Pruning|
+0342 | [Power of Four](https://leetcode.com/problems/power-of-four/) | [C++](https://github.com/kamyu104/LeetCode-Solutions/blob/master/C++/power-of-four.cpp) [Python](https://github.com/kamyu104/LeetCode-Solutions/blob/master/Python/power-of-four.py) <br>------</br> [Rust](./kamyu104/src/power_of_four.rs) | _O(1)_ | _O(1)_ | Easy | |
 
 <!-- 
 
-0342 | [Power of Four](https://leetcode.com/problems/power-of-four/) | [C++](./C++/power-of-four.cpp) [Python](./Python/power-of-four.py) | _O(1)_ | _O(1)_ | Easy | |
 0371 | [Sum of Two Integers](https://leetcode.com/problems/sum-of-two-integers/) | [C++](./C++/sum-of-two-integers.cpp) [Python](./Python/sum-of-two-integers.py) | _O(1)_ | _O(1)_ | Easy | LintCode |
 0389 | [Find the Difference](https://leetcode.com/problems/find-the-difference/) | [C++](./C++/find-the-difference.cpp) [Python](./Python/find-the-difference.py) | _O(n)_ | _O(1)_ | Easy | |
 0393 | [UTF-8 Validation](https://leetcode.com/problems/utf-8-validation/) | [C++](./C++/utf-8-validation.cpp) [Python](./Python/utf-8-validation.py) | _O(n)_ | _O(1)_ | Medium | |

kamyu104/src/main.rs

@@ -2,6 +2,7 @@ mod bitwise_and_of_numbers_range;
 mod maximum_product_of_word_lengths;
 mod missing_number;
 mod number_of_1_bits;
+mod power_of_four;
 mod power_of_two;
 mod reverse_bits;
 mod single_number;

kamyu104/src/maximum_product_of_word_lengths.rs

@@ -41,7 +41,6 @@ impl Solution2 {
     }
 }
 
-
 // # Time:  O(n) ~ O(n^2)
 // # Space: O(n)
 // https://github.com/kamyu104/LeetCode-Solutions/blob/master/Python/maximum-product-of-word-lengths.py#L1-L36
@@ -97,4 +96,4 @@ mod tests {
             0
         );
     }
-}
+}

kamyu104/src/power_of_four.rs

@@ -0,0 +1,45 @@
+// Time:  O(1)
+// Space: O(1)
+pub struct Solution1 {}
+impl Solution1 {
+    pub fn is_power_of_four(num: i32) -> bool {
+        num > 0 && (num & (num - 1)) == 0 && ((num & 0b01010101010101010101010101010101) == num)
+    }
+}
+
+// Time:  O(1)
+// Space: O(1)
+pub struct Solution2 {}
+impl Solution2 {
+    pub fn is_power_of_four(num: i32) -> bool {
+        let mut n = num;
+        while n != 0 && (n & 0b11) == 0 {
+            n >>= 2;
+        }
+        n == 1
+    }
+}
+
+// https://github.com/kamyu104/LeetCode-Solutions/blob/master/Python/power-of-four.py#L27-L34
+// pub struct Solution3 {}
+// impl Solution3 {
+//     pub fn is_power_of_four(num: i32) -> bool {
+//     }
+// }
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_is_power_of_four() {
+        assert_eq!(Solution1::is_power_of_four(16), true);
+        assert_eq!(Solution1::is_power_of_four(5), false);
+
+        assert_eq!(Solution2::is_power_of_four(16), true);
+        assert_eq!(Solution2::is_power_of_four(5), false);
+
+        // assert_eq!(Solution3::is_power_of_four(16), true);
+        // assert_eq!(Solution3::is_power_of_four(5), false);
+    }
+}