You're now a baseball game point recorder.

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

Integer (one round's score): Directly represents the number of points you get in this round.
"+" (one round's score): Represents that the points you get in this round are the sum of the last two valid round's points.
"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.
"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.

思路:用一個棧,存下所有得分,最后求和即可.

class Solution {
public:
    int calPoints(vector<string>& ops) {
        stack<int> s;
        int sum = 0;
        for (int i = 0; i < ops.size(); i++) {//遍歷ops,對每種情況處理
            if (ops[i] == "C") {
                s.pop();
            }
            else if (ops[i] == "D") {
                int tmp = s.top() * 2;
                s.push(tmp);
            }
            else if (ops[i] == "+") {
                int tmp1 = s.top();
                s.pop();
                int tmp2 = s.top() + tmp1;
                s.push(tmp1);
                s.push(tmp2);
            }
            else { // 若是數(shù)字
                int tmp = stoi(ops[i]);
                s.push(tmp);
            }
        }
        while(!s.empty()) {  //求和
            sum += s.top();
            s.pop();
        }
        return sum;
    }
};