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滑动窗口
滑动窗口有俩种:定窗口和不定窗口。滑动窗口说白了就是双指针的运用。
定窗口说明是一个特定窗口大小,通常用来解决相邻的元素,最大值,最小值。
不定窗口说的是,先由右指针去找到第一个能够符合题意的位置,记录该答案,再将左指针往后移动至不满足条件为止,此时可以刷新答案,再由右指针继续去寻找。
定窗口求最值:这个需要借助双向队列去完成。我举一个列子求项链3个元素最大值:
我们首先判断head指针是否需要出队,需要出队是说明窗口不能装下这些元素了。
继而去找,我们要的是最大值,如果当前元素值小于tai指针代指的值,直接接下去即可,但如果是大于,就要去从后往前找比他大的数字后面存储该值,并且放弃掉当前元素大于que队列里面的元素。
小于:
出队的情况
另外输出的话,我们知道当i>2时我们就需要输出队头元素,队头元素永远是当前窗口最大的元素。
所以答案是
不定窗口:
通常解决某个子串或者子序列最长或者最短。
我们还是举列子:
A串:abcddeft
B串:bd
求包含B串的A串最短子串。
首先移动j到符合题意:
发现满足题意,于是存储下来:
移动i 到 不满足题意,需要在这个过程中刷新值
就解决了,类似的问题也还是一样。