查找固定长度字符串的所有可能的子序列

def find_subsequences(string, length):
    if length == 0:
        return ['']
    if len(string) < length:
        return []
    
    subsequences = []
    for i in range(len(string)):
        char = string[i]
        remaining_string = string[i+1:]
        subseqs = find_subsequences(remaining_string, length-1)
        for subseq in subseqs:
            subsequences.append(char + subseq)
    
    return subsequences

string = "abcde"
length = 3
subsequences = find_subsequences(string, length)
print(subsequences)

['abc', 'abd', 'abe', 'acd', 'ace', 'ade', 'bcd', 'bce', 'bde', 'cde']