Added Reverse String II

Author: ryanoneill

src/lib.rs

@@ -445,7 +445,7 @@ pub mod lonely_pixel_i; // 531 ✓
 pub mod complex_number_multiplication; // 537 ✓
 
 pub mod single_element_in_a_sorted_array; // 540 ✓
-
+pub mod reverse_string_ii; // 541 ✓
 pub mod zero_one_matrix; // 542
 pub mod diameter_of_binary_tree; // 543
 

src/reverse_string_ii.rs

@@ -0,0 +1,76 @@
+/// Given a string `s` and an integer `k`, reverse the first `k` characters for every `2k`
+/// characters counting from the start of the string.
+///
+/// If there are fewer than `k` characters left, reverse all of them. If there are less than `2k`
+/// but greater than or equal to `k` characters, then reverse the first `k` characters and leave
+/// the other as original.
+struct Solution;
+
+impl Solution {
+
+    pub fn reverse_str(s: String, k: i32) -> String {
+        let mut stack = Vec::new();
+        let mut result = Vec::new();
+        let mut reversed = false;
+
+        let k = k as usize;
+        let mut index = 0;
+
+        for c in s.chars() {
+            if index % (2 * k) == 0 {
+                reversed = true;
+            } else if index % k == 0 {
+                while !stack.is_empty() {
+                    let letter = stack.pop().unwrap();
+                    result.push(letter);
+                }
+                reversed = false;
+            }
+
+            if reversed {
+                stack.push(c);
+            } else {
+                result.push(c);
+            }
+
+            index += 1;
+        }
+        while !stack.is_empty() {
+            let letter = stack.pop().unwrap();
+            result.push(letter);
+        }
+
+        result.into_iter().collect()
+    }
+
+}
+
+#[cfg(test)]
+mod tests {
+    use super::Solution;
+
+    #[test]
+    fn example_1() {
+        let s = str!("abcdefg");
+        let k = 2;
+        let result = Solution::reverse_str(s, k);
+        assert_eq!(result, "bacdfeg");
+    }
+
+    #[test]
+    fn example_2() {
+        let s = str!("abcd");
+        let k = 2;
+        let result = Solution::reverse_str(s, k);
+        assert_eq!(result, "bacd");
+    }
+
+    #[test]
+    fn example_3() {
+        let s = str!("abc");
+        let k = 4;
+        let result = Solution::reverse_str(s, k);
+        assert_eq!(result, "cba");
+    }
+
+}