Solve #227

Author: aylei

src/lib.rs

@@ -194,3 +194,4 @@ mod n0222_count_complete_tree_nodes;
 mod n0224_basic_calculator;
 mod n0225_implement_stack_using_queues;
 mod n0226_invert_binary_tree;
+mod n0227_basic_calculator_ii;

src/n0227_basic_calculator_ii.rs

@@ -0,0 +1,102 @@
+/**
+ * [227] Basic Calculator II
+ *
+ * Implement a basic calculator to evaluate a simple expression string.
+ *
+ * The expression string contains only non-negative integers, +, -, *, / operators and empty spaces  . The integer division should truncate toward zero.
+ *
+ * Example 1:
+ *
+ *
+ * Input: "3+2*2"
+ * Output: 7
+ *
+ *
+ * Example 2:
+ *
+ *
+ * Input: " 3/2 "
+ * Output: 1
+ *
+ * Example 3:
+ *
+ *
+ * Input: " 3+5 / 2 "
+ * Output: 5
+ *
+ *
+ * Note:
+ *
+ *
+ * 	You may assume that the given expression is always valid.
+ * 	Do not use the eval built-in library function.
+ *
+ *
+ */
+pub struct Solution {}
+
+// submission codes start here
+
+impl Solution {
+    pub fn calculate(s: String) -> i32 {
+        let mut acc = 0_i64;
+        let mut prev = 0_i64;
+        let mut curr = 0_i64;
+        let mut sign = 1;
+        let mut has_prev = false;
+        let mut multiple = true;
+        for ch in s.chars() {
+            match ch {
+                '0'...'9' => { curr = 10 * curr + (ch as u8 - '0' as u8) as i64; },
+                '+' | '-' => {
+                    if has_prev {
+                        if multiple {
+                            curr = prev * curr;
+                        } else {
+                            curr = prev / curr;
+                        }
+                        has_prev = false;
+                    }
+                    acc += curr * sign;
+                        curr = 0;
+                        sign = if ch == '+' { 1 } else { -1 };
+                    }
+                '*' | '/' => {
+                    if has_prev {
+                        if multiple {
+                            curr = prev * curr;
+                        } else {
+                            curr = prev / curr;
+                        }
+                    }
+                    has_prev = true;
+                    prev = curr;
+                    curr = 0;
+                    multiple = if ch == '*' { true } else { false };
+                },
+                _ => {},
+            }
+        }
+        if has_prev {
+            if multiple {
+                curr = prev * curr;
+            } else {
+                curr = prev / curr;
+            }
+        }
+        acc += sign * curr;
+        acc as i32
+    }
+}
+
+// submission codes end
+
+    #[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_227() {
+        assert_eq!(Solution::calculate("3+2*2".to_owned()), 7);
+    }
+}