Update Basic Calculator III.java

varunu28 · web-flow · commit d8655be27c20 · 2022-09-08T15:53:28.000-07:00
diff --git a/Hard/Basic Calculator III.java b/Hard/Basic Calculator III.java
@@ -1,74 +1,28 @@
 class Solution {
-    public int calculate(String s) {
-        if (s.length() == 0) {
-            return 0;
+  public int calculate(String s) {
+    int currNum = 0;
+    int prevNum = 0;
+    int result = 0;
+    char operation = '+';
+    for (int i = 0; i < s.length(); i++) {
+      char c = s.charAt(i);
+      if (Character.isDigit(c)) {
+        currNum = currNum * 10 + Character.getNumericValue(c);
+      } 
+      if ((!Character.isDigit(c) && !Character.isWhitespace(c)) || i == s.length() - 1) {
+        if (operation == '-' || operation == '+') {
+          result += prevNum;
+          prevNum = operation == '+' ? currNum : -currNum;
+        } else if (operation == '*') {
+          prevNum = prevNum * currNum;
+        } else {
+          prevNum = prevNum / currNum;
         }
-        
-        Stack<Integer> nums = new Stack<>();
-        Stack<Character> ops = new Stack<>();
-        int num = 0;
-        
-        for (int i = 0; i < s.length(); i++) {
-            char c = s.charAt(i);
-            if (c == ' ') {
-                continue;
-            }
-            
-            if (Character.isDigit(c)) {
-                num = c - '0';
-                while (i < s.length() - 1 && Character.isDigit(s.charAt(i + 1))) {
-                    num = num * 10 + (s.charAt(i + 1) - '0');
-                    i++;
-                }
-                
-                nums.push(num);
-                num = 0;
-            }
-            else if (c == '(') {
-                ops.push(c);
-            }
-            else if (c == ')') {
-                while (ops.peek() != '(') {
-                    nums.push(performOperation(ops.pop(), nums.pop(), nums.pop()));
-                }
-                ops.pop();
-            }
-            else if (c == '+' || c == '-' || c == '*' || c == '/') {
-                while (!ops.isEmpty() && precedence(c, ops.peek())) {
-                    nums.push(performOperation(ops.pop(), nums.pop(), nums.pop()));
-                }
-                
-                ops.push(c);
-            }
-        }
-        
-        while (!ops.isEmpty()) {
-            nums.push(performOperation(ops.pop(), nums.pop(), nums.pop()));
-        }
-        
-        return nums.pop();
-    }
-    
-    private int performOperation(char op, int b, int a) {
-        switch (op) {
-            case '+': return a + b;
-            case '-': return a - b;
-            case '*': return a * b;
-            case '/': return a / b;
-        }
-        
-        return 0;
-    }
-    
-    private boolean precedence(char op1, char op2) {
-        if (op2 == '(' || op2 == ')') {
-            return false;
-        }
-        
-        if ((op1 == '*' || op1 == '/') && (op2 == '+' || op2 == '-')) {
-            return false;
-        }
-        
-        return true;
+        operation = c;
+        currNum = 0;
+      }
     }
+    result += prevNum;
+    return result;
+  }
 }
