problems: add previously solved problems

Signed-off-by: Matej Focko <mfocko@redhat.com>

problems/complex-number-multiplication.rs

@@ -0,0 +1,42 @@
+use std::fmt;
+use std::str::FromStr;
+
+#[derive(Debug, PartialEq)]
+struct Complex {
+    real: i32,
+    imag: i32,
+}
+
+#[derive(Debug)]
+struct InvalidComplex;
+
+impl FromStr for Complex {
+    type Err = InvalidComplex;
+
+    fn from_str(input: &str) -> Result<Self, Self::Err> {
+        let parts: Vec<&str> = input.split('+').collect();
+        let real = parts[0].parse::<i32>().unwrap();
+        let imag = parts[1].trim_end_matches('i').parse::<i32>().unwrap();
+
+        Ok(Complex { real, imag })
+    }
+}
+
+impl fmt::Display for Complex {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{}+{}i", self.real, self.imag)
+    }
+}
+
+impl Solution {
+    pub fn complex_number_multiply(num1: String, num2: String) -> String {
+        let left: Complex = num1.parse().unwrap();
+        let right: Complex = num2.parse().unwrap();
+
+        (Complex {
+            real: left.real * right.real - left.imag * right.imag,
+            imag: left.real * right.imag + left.imag * right.real,
+        })
+        .to_string()
+    }
+}

problems/contains-duplicate.swift

@@ -0,0 +1,12 @@
+class Solution {
+    func containsDuplicate(_ nums: [Int]) -> Bool {
+        var encountered = Set<Int>()
+        for x in nums {
+            if encountered.contains(x) {
+                return true
+            }
+            encountered.insert(x)
+        }
+        return false
+    }
+}

problems/number-complement.swift

@@ -0,0 +1,13 @@
+class Solution {
+    func findComplement(_ num: Int) -> Int {
+        if num == 0 {
+            return 0;
+        }
+
+        if num & 1 != 0 {
+            return findComplement(num >> 1) << 1;
+        }
+
+        return (findComplement(num >> 1) << 1) + 1;
+    }
+}