Added remove k digits solution.

README.md

@@ -250,7 +250,8 @@ programming challenges completed in other languages.
 - Most Beautiful Item for Each Query (https://leetcode.com/problems/most-beautiful-item-for-each-query)
 - Count Number of Fair Pairs(https://leetcode.com/problems/count-the-number-of-fair-pairs)
 - Sum of Square Numbers (https://leetcode.com/problems/sum-of-square-numbers)
-_ Minimized Maximum of Products Distributed to Any Store (https://leetcode.com/problems/minimized-maximum-of-products-distributed-to-any-store)
+- Minimized Maximum of Products Distributed to Any Store (https://leetcode.com/problems/minimized-maximum-of-products-distributed-to-any-store)
+- Remove K Digits (https://leetcode.com/problems/remove-k-digits)
 
 #### Hard
 

src/leetcode/mod.rs

@@ -98,3 +98,4 @@ mod max_beauty;
 mod count_fair_pairs;
 mod square_numbers;
 mod minimized_maximum;
+mod remove_k_digits;

src/leetcode/remove_k_digits.rs

@@ -0,0 +1,46 @@
+pub fn remove_kdigits(number: String, k: i32) -> String {
+    let mut k = k as usize;
+    let mut stack = String::with_capacity(number.len() - k);
+    for digit in number.chars() {
+        while k > 0 && !stack.is_empty() && digit < stack.chars().last().unwrap() {
+            // Remove digits larger than the current one.
+            stack.pop();
+            k -= 1;
+        }
+        if stack.is_empty() && digit == '0' {
+            // Skip leading zeros.
+            continue;
+        }
+        stack.push(digit);
+    }
+
+    // Remove any remaining right digits if not all digits were removed in the main loop.
+    for _ in 0..k {
+        stack.pop();
+    }
+
+    match stack.is_empty() {
+        true => "0".to_string(),
+        false => stack,
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::remove_kdigits;
+
+    #[test]
+    fn removes_k_digits_to_achieve_smallest_number_possible() {
+        assert_eq!("1219".to_string(), remove_kdigits("1432219".to_string(), 3))
+    }
+
+    #[test]
+    fn digits_with_trailing_zeros() {
+        assert_eq!("200".to_string(), remove_kdigits("10200".to_string(), 1))
+    }
+
+    #[test]
+    fn remove_all_digits() {
+        assert_eq!("0".to_string(), remove_kdigits("10".to_string(), 2))
+    }
+}