Add 224_Basic_Calculator.java

Author: seanprashad

Strings/224_Basic_Calculator.java

@@ -0,0 +1,47 @@
+class Solution {
+    public int calculate(String s) {
+        if (s.isEmpty()) {
+            return 0;
+        }
+
+        int result = 0, sign = 1;
+
+        Stack<Integer> st = new Stack<>();
+
+        for (int i = 0; i < s.length(); i++) {
+            char c = s.charAt(i);
+
+            if (c == ' ') {
+                continue;
+            }
+
+            if (Character.isDigit(c)) {
+                int sum = c - '0';
+
+                while (i + 1 < s.length() && Character.isDigit(s.charAt(i + 1))) {
+                    sum = sum * 10 + s.charAt(i + 1) - '0';
+                    ++i;
+                }
+
+                result = result + sum * sign;
+            } else if (c == '+') {
+                sign = 1;
+            } else if (c == '-') {
+                sign = -1;
+            } else if (c == '(') {
+                st.push(result);
+                st.push(sign);
+
+                result = 0;
+                sign = 1;
+            } else if (c == ')') {
+                int prevSign = st.pop();
+                int prevResult = st.pop();
+
+                result = result * prevSign + prevResult;
+            }
+        }
+
+        return result;
+    }
+}