AB*A Changing

AtCoder

IDagc069_c

Time2000ms

Memory256MB

Difficulty—

You are given two strings $S$ and $T$ of length $N$ consisting of `A` and `B`. Let $s_i$ denote the $i$\-th character of $S$. You can perform the following operation on $S$ any number of times, possibly zero: * Choose an integer pair $(i, j)$ satisfying the following conditions: * $1 \leq i < j \leq N$ * $s_i = s_j = $ `A` * $s_{i+1} = s_{i+2} = \ldots = s_{j-1} = $ `B` * Then, simultaneously replace each of $s_i, s_{i+1}, \ldots, s_j$ with the other character (`A` becomes `B`, and `B` becomes `A`). Determine the minimum number of operations required to make $S$ equal to $T$. If it is impossible, print `-1`. ## Constraints * $1 \leq N \leq 2 \times 10^5$ * $S$ and $T$ are strings of length $N$ consisting of `A` and `B`. ## Input The input is given from Standard Input in the following format: $N$ $S$ $T$ [samples]

Samples

Input #1

5
AAABA
BAAAB

Output #1

2

You can make $S$ equal to $T$ in two operations as follows:

1.  Perform the operation with $(i, j) = (2, 3)$. $S$ becomes `ABBBA`.
2.  Perform the operation with $(i, j) = (1, 5)$. $S$ becomes `BAAAB`.

It is impossible to make $S$ equal to $T$ in fewer than two operations, so the answer is `2`.

Input #2

1
A
B

Output #2

\-1

It is impossible to make $S$ equal to $T$. Note that you must choose $(i, j)$ with $i < j$.

Input #3

1
A
A

Output #3

0

Without any operation, $S$ is already equal to $T$.

Input #4

10
AAABBABAAB
BBABBAAABB

Output #4

API Response (JSON)

{
  "problem": {
    "name": "AB*A Changing",
    "description": {
      "content": "You are given two strings $S$ and $T$ of length $N$ consisting of `A` and `B`. Let $s_i$ denote the $i$\\-th character of $S$. You can perform the following operation on $S$ any number of times, possib",
      "description_type": "Markdown"
    },
    "platform": "AtCoder",
    "limit": {
      "time_limit": 2000,
      "memory_limit": 262144
    },
    "difficulty": "None",
    "is_remote": true,
    "is_sync": true,
    "sync_url": null,
    "sign": "agc069_c"
  },
  "statements": [
    {
      "statement_type": "Markdown",
      "content": "You are given two strings $S$ and $T$ of length $N$ consisting of `A` and `B`. Let $s_i$ denote the $i$\\-th character of $S$.\nYou can perform the following operation on $S$ any number of times, possib...",
      "is_translate": false,
      "language": "English"
    }
  ]
}

Full JSON Raw Segments