附一下python版的1 2题 第三题完全没有思路 n = int(input().strip()) num = input().strip() target = num[-1] start = num[0] dp = [1]*len(num) dp[0] = 0 memo = {} if start == target: print(1) else: res = 0 memo[num[0]] = 0 for i in range(1,len(num)): if num[i] not in memo: memo[num[i]] = dp[i-1]+1 dp[i] = min(dp[i-1]+1,memo[num[i]]+1) if dp[i] < memo[num[i]]: memo[num[i]] = dp[i] print(dp[-1])