LeetCode [栈] 682.Baseball Game（C++和Python实现）

682 Baseball Game [难度：简单] [stringstream:字符串转整数神器]

【题目】

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 validround'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.

【题解C++】

既然是和最近的分数有关，那就是栈的思想啦~写这道题才发现stringstream这个字符串和整数相互转换的好东西！要找个时间好好整理下字符串相关的写题神器了，不然还得像以前一样吭哧吭哧自己造轮子= = 

class Solution {
public:
    //要小心，这里是二维数组，因为数字可能是两位以上~
    //所以ops[i]其实是一个string类型而不是字符
    int calPoints(vector<string>& ops) {
        stack<int> st;
        int sum = 0;
        for(int i=0;i<ops.size();i++)
        {
            //别忘了把pop出去的两个数再push回来
            if(ops[i]=="+")
            {
                int top1 = st.top();
                st.pop();
                int top2 = st.top();
                st.pop();
                sum += top1+top2;
                st.push(top2);
                st.push(top1);
                st.push(top1+top2);
            }
            else if(ops[i]=="D")
            {
                sum += st.top()*2;
                st.push(st.top()*2);
            }
            else if(ops[i]=="C")
            {
                sum -= st.top();
                st.pop();
            }
            //stringstream字符串转换为整型
            else
            {
                stringstream ss;
                ss<<ops[i];
                int tmp;
                ss>>tmp;
                sum += tmp;
                st.push(tmp);
            }
        }
        return sum;
    }
};

【解题Python】

 思路同C++。

class Solution:
    def calPoints(self, ops: List[str]) -> int:
        st = []
        for i in ops:
            if i=='+':
                st.append(st[-1]+st[-2])
            elif i=='D':
                st.append(st[-1]*2)
            elif i=='C':
                st.pop(-1)
            else:
                st.append(int(i))
        return sum(st)