Leetcode 495 Teemo Attacking

题目

In LOL world, there is a hero called Teemo and his attacking can make his enemy Ashe be in poisoned condition. Now, given the Teemo’s attacking ascending time series towards Ashe and the poisoning time duration per Teemo’s attacking, you need to output the total time that Ashe is in poisoned condition.

You may assume that Teemo attacks at the very beginning of a specific time point, and makes Ashe be in poisoned condition immediately.

Example 1:
Input: [1,4], 2
Output: 4
Explanation: At time point 1, Teemo starts attacking Ashe and makes Ashe be poisoned immediately.
This poisoned status will last 2 seconds until the end of time point 2.
And at time point 4, Teemo attacks Ashe again, and causes Ashe to be in poisoned status for another 2 seconds.
So you finally need to output 4.

Example 2:
Input: [1,2], 2
Output: 3
Explanation: At time point 1, Teemo starts attacking Ashe and makes Ashe be poisoned.
This poisoned status will last 2 seconds until the end of time point 2.
However, at the beginning of time point 2, Teemo attacks Ashe again who is already in poisoned status.
Since the poisoned status won’t add up together, though the second poisoning attack will still work at time point 2, it will stop at the end of time point 3.
So you finally need to output 3.

Note:
You may assume the length of given time series array won’t exceed 10000.
You may assume the numbers in the Teemo’s attacking time series and his poisoning time duration per attacking are non-negative integers, which won’t exceed 10,000,000.

思路

第i个数timeSeries[i]会导致$I=[timeSeries[i],timeSeries[i]+duration)$这个区间内是被poison的，考虑下一个数timeSeries[i+1]，因为输入是一组递增的数，这时下一个数只能属于区间$I$或者是比区间$I$要大。用两个变量left和right记录当前的被poison的区间，原来是$I$的左右段，如果下一个数属于$I$，那么这两个poison区间有重叠，直接更新右端right值，此时left和right记录的区间是重叠后区间的并集；如果下一个数不属于$I$，也就是timeSeries[i+1] > right时，这时更新中毒的时长，加上之前的区间长度right-left，然后充值区间左右端的值。最后循环结束还需加上最后一次的区间长度。代码如下。

代码

class Solution {
    public int findPoisonedDuration(int[] timeSeries, int duration) {
        if (timeSeries == null || timeSeries.length == 0) return 0;
        int res = 0;
        int left = timeSeries[0], right = timeSeries[0];
        for (int num : timeSeries) {
            if (num > right) {
                res += right - left;
                left = num;
            }
            right = num + duration;
        }
        res += right - left;
        return res;
    }
}