小黑代码

class Solution:
    def checkInclusion(self, s1: str, s2: str) -> bool:
        # 字符串长度
        n_s1 = len(s1)
        n_s2 = len(s2)
        if n_s1 > n_s2:
            return False
        # s1的字符计数字典
        count_s1 = [0] * 26
        # 窗口计数字典
        count_window = [0] * 26
        # 寻找初始窗口
        for i in range(n_s1):
            count_s1[ord(s1[i])-97] += 1
            count_window[ord(s2[i])-97] += 1
        # 初始条件是否符合
        if count_s1 == count_window:
            return True
        for i in range(n_s1, n_s2):
            count_window[ord(s2[i])-97] += 1
            count_window[ord(s2[i-n_s1])-97] -= 1
            if count_s1 == count_window:
                return True
        return False

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滑动窗口法

class Solution:
    def checkInclusion(self, s1: str, s2: str) -> bool:
        # 字符串长度
        n_s1 = len(s1)
        n_s2 = len(s2)
        if n_s1 > n_s2:
            return False
        # 差值字典
        diff_map = [0] * 26
        # 计算初始窗口差值
        for i in range(n_s1):
            diff_map[ord(s1[i])-97] += 1
            diff_map[ord(s2[i])-97] -= 1
        # 计算差值
        diff = sum([abs(i) for i in diff_map])
        if not diff:
            return True
        # 开始滑动窗口
        for i in range(n_s1, n_s2):
            # 窗口头部字符在差值大于0
            if diff_map[ord(s2[i-n_s1])-97] >= 0:
                diff += 1
            else:
                diff -= 1
            diff_map[ord(s2[i-n_s1])-97] += 1
            # 窗口尾部字符在差值大于0
            if diff_map[ord(s2[i])-97] > 0:
                diff -= 1
            else:
                diff += 1
            diff_map[ord(s2[i])-97] -= 1
            if not diff:
                return True
        return False

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双指针

class Solution:
    def checkInclusion(self, s1: str, s2: str) -> bool:
        # 字符串长度
        n_s1 = len(s1)
        n_s2 = len(s2)
        if n_s1 > n_s2:
            return False
        # 差值数组
        diff_map = [0] * 26
        for i in range(n_s1):
            diff_map[ord(s1[i])-97] -= 1
        # 开始进行双指针操作
        left = 0
        right = 0
        while right < n_s2:
            # left右移动
            while diff_map[ord(s2[right])-97] >= 0:
                diff_map[ord(s2[left])-97] -= 1
                left += 1
            diff_map[ord(s2[right])-97] += 1
            right += 1
            if right - left == n_s1:
                return True
        return False