problems(rs): add “946. Validate Stack Sequences”

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

problems/validate-stack-sequences.rs

@@ -0,0 +1,56 @@
+struct Solution {}
+impl Solution {
+    pub fn validate_stack_sequences(pushed: Vec<i32>, popped: Vec<i32>) -> bool {
+        let mut stack: Vec<i32> = vec![];
+
+        let mut i = 0;
+        let mut j = 0;
+
+        loop {
+            // If the top is to be popped, pop it
+            if let Some(&top) = stack.last() {
+                if j < popped.len() && top == popped[j] {
+                    stack.pop();
+                    j += 1;
+                    continue;
+                }
+            }
+
+            // If I have an element that can be pushed, push it
+            if i < pushed.len() {
+                stack.push(pushed[i]);
+                i += 1;
+                continue;
+            }
+
+            // If I can't pop nor push, it's done or screwed up
+            break;
+        }
+
+        // If it's correct simulation, stack must be empty
+        stack.is_empty()
+    }
+}
+
+fn main() {}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn success() {
+        assert!(Solution::validate_stack_sequences(
+            vec![1, 2, 3, 4, 5],
+            vec![4, 5, 3, 2, 1]
+        ));
+    }
+
+    #[test]
+    fn fail() {
+        assert!(!Solution::validate_stack_sequences(
+            vec![1, 2, 3, 4, 5],
+            vec![4, 3, 5, 1, 2]
+        ));
+    }
+}