{ "data": { "question": { "questionId": "1941", "questionFrontendId": "1830", "boundTopicId": null, "title": "Minimum Number of Operations to Make String Sorted", "titleSlug": "minimum-number-of-operations-to-make-string-sorted", "content": "

You are given a string s (0-indexed)​​​​​​. You are asked to perform the following operation on s​​​​​​ until you get a sorted string:

\n\n
    \n\t
  1. Find the largest index i such that 1 <= i < s.length and s[i] < s[i - 1].
  2. \n\t
  3. Find the largest index j such that i <= j < s.length and s[k] < s[i - 1] for all the possible values of k in the range [i, j] inclusive.
  4. \n\t
  5. Swap the two characters at indices i - 1​​​​ and j​​​​​.
  6. \n\t
  7. Reverse the suffix starting at index i​​​​​​.
  8. \n
\n\n

Return the number of operations needed to make the string sorted. Since the answer can be too large, return it modulo 109 + 7.

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Example 1:

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\nInput: s = "cba"\nOutput: 5\nExplanation: The simulation goes as follows:\nOperation 1: i=2, j=2. Swap s[1] and s[2] to get s="cab", then reverse the suffix starting at 2. Now, s="cab".\nOperation 2: i=1, j=2. Swap s[0] and s[2] to get s="bac", then reverse the suffix starting at 1. Now, s="bca".\nOperation 3: i=2, j=2. Swap s[1] and s[2] to get s="bac", then reverse the suffix starting at 2. Now, s="bac".\nOperation 4: i=1, j=1. Swap s[0] and s[1] to get s="abc", then reverse the suffix starting at 1. Now, s="acb".\nOperation 5: i=2, j=2. Swap s[1] and s[2] to get s="abc", then reverse the suffix starting at 2. Now, s="abc".\n
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Example 2:

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\nInput: s = "aabaa"\nOutput: 2\nExplanation: The simulation goes as follows:\nOperation 1: i=3, j=4. Swap s[2] and s[4] to get s="aaaab", then reverse the substring starting at 3. Now, s="aaaba".\nOperation 2: i=4, j=4. Swap s[3] and s[4] to get s="aaaab", then reverse the substring starting at 4. Now, s="aaaab".\n
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Constraints:

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