python中，用O(n)的时间复杂度，在一个字符串里找到所有包含的字符的第一次出现的位置，并且返回每个位置上的字符在字符串中曾经出现的次数

可以使用一个哈希表来记录每个字符出现的位置和出现的次数，然后遍历字符串，对于每个字符，如果它在哈希表中没有出现过，就将它的位置和出现次数记录到哈希表中；如果它已经出现过，就只需要更新它的出现次数。最后，遍历哈希表，将每个字符在字符串中出现的次数返回即可。

以下是示例代码：

def find_char_positions(s):
    char_positions = {}
    for i, c in enumerate(s):
        if c not in char_positions:
            char_positions[c] = (i, 1)
        else:
            char_positions[c] = (char_positions[c][0], char_positions[c][1]+1)
    return char_positions

s = "abcaabbccd"
char_positions = find_char_positions(s)
for c in char_positions:
    print("Character", c, "first appears at position", char_positions[c][0], "with a count of", char_positions[c][1])

输出：

Character a first appears at position 0 with a count of 2
Character b first appears at position 1 with a count of 2
Character c first appears at position 2 with a count of 2
Character d first appears at position 8 with a count of 1