feat: add min stack problem solution

Author: bujosa

src/easy/min_stack.rs

@@ -0,0 +1,68 @@
+#![allow(dead_code)]
+struct MinStack {
+    stack: Vec<i32>,
+    min_stack: Vec<i32>,
+}
+
+/**
+ * `&self` means the method takes an immutable reference.
+ * If you need a mutable reference, change it to `&mut self` instead.
+ */
+impl MinStack {
+    fn new() -> Self {
+        MinStack {
+            stack: Vec::new(),
+            min_stack: Vec::new(),
+        }
+    }
+
+    fn push(&mut self, val: i32) {
+        self.stack.push(val);
+        if self.min_stack.is_empty() || val <= self.min_stack[self.min_stack.len() - 1] {
+            self.min_stack.push(val);
+        }
+    }
+
+    fn pop(&mut self) {
+        let val = self.stack.pop().unwrap();
+        if val == self.min_stack[self.min_stack.len() - 1] {
+            self.min_stack.pop();
+        }
+    }
+
+    fn top(&self) -> i32 {
+        self.stack[self.stack.len() - 1]
+    }
+
+    fn get_min(&self) -> i32 {
+        self.min_stack[self.min_stack.len() - 1]
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_155() {
+        let mut obj = MinStack::new();
+        obj.push(-2);
+        obj.push(0);
+        obj.push(-3);
+        assert_eq!(obj.get_min(), -3);
+        obj.pop();
+        assert_eq!(obj.top(), 0);
+        assert_eq!(obj.get_min(), -2);
+    }
+
+    #[test]
+    fn test_155_2() {
+        let mut obj = MinStack::new();
+        obj.push(0);
+        obj.push(1);
+        obj.push(0);
+        assert_eq!(obj.get_min(), 0);
+        obj.pop();
+        assert_eq!(obj.get_min(), 0);
+    }
+}