682. 棒球比赛

🟢 🔖 栈 数组 模拟 🔗 力扣open in new window LeetCodeopen in new window

题目

You are keeping the scores for a baseball game with strange rules. At the beginning of the game, you start with an empty record.

You are given a list of strings operations, where operations[i] is the ith operation you must apply to the record and is one of the following:

An integer x: Record a new score of x.
'+': Record a new score that is the sum of the previous two scores.
'D': Record a new score that is the double of the previous score.
'C': Invalidate the previous score, removing it from the record.

Return the sum of all the scores on the record after applying all the operations.

The test cases are generated such that the answer and all intermediate calculations fit in a 32-bit integer and that all operations are valid.

Example 1:

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.

Example 2:

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.

Example 3:

Input: ops = ["1","C"]
Output: 0
Explanation:
"1" - Add 1 to the record, record is now [1].
"C" - Invalidate and remove the previous score, record is now [].
Since the record is empty, the total sum is 0.

Constraints:

1 <= operations.length <= 1000
operations[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.

题目大意

这道题是模拟题，给一串数字和操作符。出现数字就直接累加，出现 "C" 就代表栈推出一个元素，相应的总和要减去栈顶的元素。出现 "D" 就代表把前一个元素乘以 2，就得到当前的元素值，再累加。出现 "+" 就代表把前 2 个值求和，得到当前元素的值，再累积。

解题思路

这道题用栈模拟即可。

代码

/**
 * @param {string[]} operations
 * @return {number}
 */
var calPoints = function (operations) {
	let stack = [];
	for (item of operations) {
		let top = stack.length - 1;
		switch (item) {
			case '+':
				stack.push(stack[top] + stack[top - 1]);
				break;
			case 'C':
				stack.pop();
				break;
			case 'D':
				stack.push(stack[top] * 2);
				break;
			default:
				stack.push(Number(item));
				break;
		}
	}
	return stack.reduce((a, b) => a + b, 0);
};

682. 棒球比赛

# 682. 棒球比赛

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682. 棒球比赛

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