> For the complete documentation index, see [llms.txt](https://hao-fu-1.gitbook.io/oj/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://hao-fu-1.gitbook.io/oj/array_and_numbers/1332.-remove-palindromic-subsequences.md).

# 1332. Remove Palindromic Subsequences

Given a string `s` consisting only of letters `'a'` and `'b'`. In a single step you can remove one palindromic **subsequence** from `s`.

Return the minimum number of steps to make the given string empty.

A string is a subsequence of a given string, if it is generated by deleting some characters of a given string without changing its order.

A string is called palindrome if is one that reads the same backward as well as forward.

**Example 1:**

```
Input: s = "ababa"
Output: 1
Explanation: String is already palindrome
```

**Example 2:**

```
Input: s = "abb"
Output: 2
Explanation: "abb" -> "bb" -> "". 
Remove palindromic subsequence "a" then "bb".
```

**Example 3:**

```
Input: s = "baabb"
Output: 2
Explanation: "baabb" -> "b" -> "". 
Remove palindromic subsequence "baab" then "b".
```

**Example 4:**

```
Input: s = ""
Output: 0
```

只由a和b组成的字符串s每步能移除掉一个回文序列，问把整个字符串清空至少需要多少步。分为三种情况：1. 空字符串，返回0；2. s本身已是回文，返回1；3. 其它，第一步清掉所有的a，第二步清掉b，最多需要两步。

```cpp
class Solution {
public:
    int removePalindromeSub(string s) {
        const int N = s.length();
        if (N == 0) return 0;
        bool pal = true; 
        for (int i = 0, j = N - 1; i < j; ++i, --j) {
            if (s[i] != s[j]) {
                pal = false;
                break;
            }
        }
        if (pal) return 1;
        return 2;
    }
};
```