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The hostel mess wants a small calculator for its bills. A clerk types an expression the normal way, such as 2 + 3 * ( 10 - 4 ), and the calculator must print its value.
Use the usual rules. Brackets are worked out first. Then * and / come before + and -. Operators of the same level go from left to right, so 10 - 4 - 3 is 3. Division keeps only the whole part and drops the rest toward zero, like Java's / on whole numbers: 7 / 2 is 3 and -7 / 2 is -3.
+, -, *, /, or a bracket ( or ).Example 1
Input
2 + 3 * ( 10 - 4 )
Output
20
The bracket gives 6, then 3 × 6 = 18, then 2 + 18 = 20.
Example 2
Input
10 - 4 - 3
Output
3
Same level, left to right: (10 - 4) - 3 = 3.
Try the problem first. Open one hint at a time.
Use two stacks: one for numbers and one for operators and opening brackets.
Before you push a new operator, first work out every operator on the stack that has the same or a higher level, until you meet a (.
To work out one operator, pop it and the top two numbers. The top number is the right-hand value. Push the result.
For ), work out operators until the ( and then remove the (. At the end, work out everything left. Use long for the values.
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