DAY 29
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# 682. Baseball Game

## Question

You are keeping score for a baseball game with strange rules. The game consists of several rounds, where the scores of past rounds may affect future rounds' scores.

At the beginning of the game, you start with an empty record. You are given a list of strings `ops`, where `ops[i]` is the `ith` operation you must apply to the record and is one of the following:

1. An integer `x` - Record a new score of `x`.
2. `"+"` - Record a new score that is the sum of the previous two scores. It is guaranteed there will always be two previous scores.
3. `"D"` - Record a new score that is double the previous score. It is guaranteed there will always be a previous score.
4. `"C"` - Invalidate the previous score, removing it from the record. It is guaranteed there will always be a previous score.

Return the sum of all the scores on the record.

## Example

### Example1

``````Input: ops = ["5","2","C","D","+"]
Output: 30
Explanation:
"5" - Add 5 to the record, record is now [5].
"2" - Add 2 to the record, record is now [5, 2].
"C" - Invalidate and remove the previous score, record is now [5].
"D" - Add 2 * 5 = 10 to the record, record is now [5, 10].
"+" - Add 5 + 10 = 15 to the record, record is now [5, 10, 15].
The total sum is 5 + 10 + 15 = 30.
``````

### Example2

``````Input: ops = ["5","-2","4","C","D","9","+","+"]
Output: 27
Explanation:
"5" - Add 5 to the record, record is now [5].
"-2" - Add -2 to the record, record is now [5, -2].
"4" - Add 4 to the record, record is now [5, -2, 4].
"C" - Invalidate and remove the previous score, record is now [5, -2].
"D" - Add 2 * -2 = -4 to the record, record is now [5, -2, -4].
"9" - Add 9 to the record, record is now [5, -2, -4, 9].
"+" - Add -4 + 9 = 5 to the record, record is now [5, -2, -4, 9, 5].
"+" - Add 9 + 5 = 14 to the record, record is now [5, -2, -4, 9, 5, 14].
The total sum is 5 + -2 + -4 + 9 + 5 + 14 = 27.
``````

### Example3

``````Input: ops = ["1"]
Output: 1
``````

### Constraints

• `1 <= ops.length <= 1000`
• `ops[i]` is `"C"`, `"D"`, `"+"`, or a string representing an integer in the range `[-3 * 10^4, 3 * 10^4]`.
• For operation `"+"`, there will always be at least two previous scores on the record.
• For operations `"C"` and `"D"`, there will always be at least one previous score on the record.

## 解題

### Think

• 就照著題目的規則去用if判斷式處理，但是因為`isnumeric()`只能判斷0~9之間的String，所以多用了一個if來判斷有沒有`-`號，有的話，把`minus_flag`設成`True`，進到記錄數字的判斷式一樣直接記錄下來。
• 最後回傳記錄陣列的數字總和。

### Code

#### Python

``````class Solution:
def calPoints(self, ops: List[str]) -> int:
record = []
record_index = 0
minus_flag = False

for index in range(len(ops)):
if ops[index][0] == "-":
minus_flag = True

if ops[index].isnumeric() or minus_flag:
record.append(int(ops[index]))
minus_flag = False
record_index += 1

elif ops[index] == "+":
record.append((int(record[record_index-2])+int(record[record_index-1])))
record_index += 1

elif ops[index] == "D":
record.append((int(record[record_index-1])*2))
record_index += 1

elif ops[index] == "C":
record.pop(-1)
record_index -= 1

return sum(record)
``````

### Result

• Python

30天 Leetcode解題之路30