solve #150

Author: aylei

src/lib.rs

@@ -144,3 +144,4 @@ mod n0146_lru_cache;
 mod n0147_insertion_sort_list;
 mod n0148_sort_list;
 mod n0149_max_points_on_a_line;
+mod n0150_evaluate_reverse_polish_notation;

src/n0150_evaluate_reverse_polish_notation.rs

@@ -0,0 +1,86 @@
+/**
+ * [150] Evaluate Reverse Polish Notation
+ *
+ * Evaluate the value of an arithmetic expression in <a href="http://en.wikipedia.org/wiki/Reverse_Polish_notation" target="_blank">Reverse Polish Notation</a>.
+ * 
+ * Valid operators are +, -, *, /. Each operand may be an integer or another expression.
+ * 
+ * Note:
+ * 
+ * 
+ * 	Division between two integers should truncate toward zero.
+ * 	The given RPN expression is always valid. That means the expression would always evaluate to a result and there won't be any divide by zero operation.
+ * 
+ * 
+ * Example 1:
+ * 
+ * 
+ * Input: ["2", "1", "+", "3", "*"]
+ * Output: 9
+ * Explanation: ((2 + 1) * 3) = 9
+ * 
+ * 
+ * Example 2:
+ * 
+ * 
+ * Input: ["4", "13", "5", "/", "+"]
+ * Output: 6
+ * Explanation: (4 + (13 / 5)) = 6
+ * 
+ * 
+ * Example 3:
+ * 
+ * 
+ * Input: ["10", "6", "9", "3", "+", "-11", "*", "/", "*", "17", "+", "5", "+"]
+ * Output: 22
+ * Explanation: 
+ *   ((10 * (6 / ((9 + 3) * -11))) + 17) + 5
+ * = ((10 * (6 / (12 * -11))) + 17) + 5
+ * = ((10 * (6 / -132)) + 17) + 5
+ * = ((10 * 0) + 17) + 5
+ * = (0 + 17) + 5
+ * = 17 + 5
+ * = 22
+ * 
+ * 
+ */
+pub struct Solution {}
+
+// submission codes start here
+
+impl Solution {
+    pub fn eval_rpn(tokens: Vec<String>) -> i32 {
+        let mut stack: Vec<i32> = Vec::new();
+        for t in tokens.iter() {
+            if let Ok(num) = t.parse::<i32>() {
+                stack.push(num);
+            } else {
+                let right = stack.pop().unwrap();
+                let left = stack.pop().unwrap();
+                match (t as &str) {
+                    "*" => { stack.push(left * right) },
+                    "+" => { stack.push(left + right) },
+                    "/" => { stack.push(left / right) },
+                    "-" => { stack.push(left - right) },
+                    _ => { unreachable!() },
+                }
+            }
+        }
+        stack.pop().unwrap()
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_150() {
+        assert_eq!(
+            Solution::eval_rpn(vec_string!["10", "6", "9", "3", "+", "-11", "*", "/", "*", "17", "+", "5", "+"]),
+            22
+        );
+    }
+}