Baseball Game问题及解法

本文主要是介绍Baseball Game问题及解法，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

问题描述：

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.

示例:

Input: ["5","2","C","D","+"]
Output: 15
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.

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.

问题分析：

对于不同的string，执行相应的操作，注意保存好最后一个有效比分和前一个有效比分，（建议将有效比分全部保留）。

过程详见代码：

class Solution {
public:int calPoints(vector<string>& ops) {vector<int> res;int sum = 0, score = 0;for (int i = 0; i < ops.size(); i++){if (ops[i] == "C"){score = -res.back();res.pop_back();}else if (ops[i] == "D"){score = 2 * res.back();res.emplace_back(score);}else if (ops[i] == "+"){int len = res.size();score = res[len - 1] + res[len - 2];res.emplace_back(score);}else{score = stoi(ops[i]);res.emplace_back(score);}sum += score;}return sum;}
};

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