[LeetCode] 682. Baseball Game 棒球游戏

You're now a baseball game point recorder.

Given a list of strings, each string can be one of the 4 following types:

1. Integer (one round's score): Directly represents the number of points you get in this round.
2. "+" (one round's score): Represents that the points you get in this round are the sum of the last two valid round's points.
3. "D" (one round's score): Represents that the points you get in this round are the doubled data of the last valid round's points.
4. "C" (an operation, which isn't a round's score): Represents the last valid round's points you get were invalid and should be removed.

Each round's operation is permanent and could have an impact on the round before and the round after.

You need to return the sum of the points you could get in all the rounds.

Example 1:

Input: ["5","2","C","D","+"]
Output: 30
Explanation: 
Round 1: You could get 5 points. The sum is: 5.
Round 2: You could get 2 points. The sum is: 7.
Operation 1: The round 2's data was invalid. The sum is: 5.  
Round 3: You could get 10 points (the round 2's data has been removed). The sum is: 15.
Round 4: You could get 5 + 10 = 15 points. The sum is: 30.

Example 2:

Input: ["5","-2","4","C","D","9","+","+"]
Output: 27
Explanation: 
Round 1: You could get 5 points. The sum is: 5.
Round 2: You could get -2 points. The sum is: 3.
Round 3: You could get 4 points. The sum is: 7.
Operation 1: The round 3's data is invalid. The sum is: 3.  
Round 4: You could get -4 points (the round 3's data has been removed). The sum is: -1.
Round 5: You could get 9 points. The sum is: 8.
Round 6: You could get -4 + 9 = 5 points. The sum is 13.
Round 7: You could get 9 + 5 = 14 points. The sum is 27.

Note:

• The size of the input list will be between 1 and 1000.
• Every integer represented in the list will be between -30000 and 30000.

解法：栈，用一个stack记录，循环字符串，如果是数字直接进栈，如果当前字符是操作符对栈里面的数字进行相应处理，'+'把栈里面最后两个数字相加然后如栈，'D'把栈里的最后一个数字乘以2然后如栈，'C'移除栈里面的最后一个元素。最后返回栈里所有元素的和。

Java:

class Solution {
    public int calPoints(String[] ops) {
        int sum = 0;
        LinkedList<Integer> list = new LinkedList<>();
        for (String op : ops) {
            if (op.equals("C")) {
                sum -= list.removeLast();
            }
            else if (op.equals("D")) {
                list.add(list.peekLast() * 2);
                sum += list.peekLast();
            }
            else if (op.equals("+")) {
                list.add(list.peekLast() + list.get(list.size() - 2));
                sum += list.peekLast();
            }
            else {
                list.add(Integer.parseInt(op));
                sum += list.peekLast();
            }
        }
        return sum;
    }
}　　

Python:

class Solution(object):
    def calPoints(self, ops):
        """
        :type ops: List[str]
        :rtype: int
        """
        history = []
        for op in ops:
            if op == '+':
                history.append(history[-1] + history[-2])
            elif op == 'D':
                history.append(history[-1] * 2)
            elif op == 'C':
                history.pop()
            else:
                history.append(int(op))
        return sum(history)　　

C++:

class Solution {
public:
    int calPoints(vector<string>& ops) {
        vector<int> v;
        for (string op : ops) {
            if (op == "+") {
                v.push_back(v.back() + v[v.size() - 2]);
            } else if (op == "D") {
                v.push_back(2 * v.back());
            } else if (op == "C") {
                v.pop_back();
            } else {
                v.push_back(stoi(op));
            }
        }
        return accumulate(v.begin(), v.end(), 0);
    }
};

　　

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