Add 227_Basic_Calculator_II.java

Author: Sean Prashad

Strings/227_Basic_Calculator_II.java

@@ -0,0 +1,44 @@
+class Solution {
+    public int calculate(String s) {
+        if (s == null || s.length() == 0) {
+            return 0;
+        }
+
+        Stack<Integer> st = new Stack<>();
+        int num = 0, total = 0;
+        char sign = '+';
+
+        for (int i = 0; i < s.length(); i++) {
+            char c = s.charAt(i);
+
+            if (Character.isDigit(c)) {
+                num = num * 10 + c - '0';
+            }
+
+            if (i == s.length() - 1 || !Character.isDigit(c) && c != ' ') {
+                switch (sign) {
+                    case '+':
+                        st.push(num);
+                        break;
+                    case '-':
+                        st.push(-num);
+                        break;
+                    case '*':
+                        st.push(st.pop() * num);
+                        break;
+                    case '/':
+                        st.push(st.pop() / num);
+                        break;
+                }
+
+                sign = c;
+                num = 0;
+            }
+        }
+
+        while (!st.isEmpty()) {
+            total += st.pop();
+        }
+        return total;
+    }
+}