HardNo. 1830
Minimum Number of Operations to Make String Sorted — LeetCode 1830 Python Solution
- Pattern
- Math and Number Theory
- Topics
- Math, String, Combinatorics
- Reading time
- 5 min
- Source
- leetcode.com
The problem
You are given a string s (0-indexed). You are asked to perform the following operation on s until you get a sorted string: Find the largest index i such that 1 <= i < s.length and s[i] < s[i - 1].
Example
- Input
- s = "cba"
- Output
- 5
- Explanation
- The simulation goes as follows:
Python solution
n = 3010
mod = 10**9 + 7
f = [1] + [0] * n
g = [1] + [0] * n
for i in range(1, n):
f[i] = f[i - 1] * i % mod
g[i] = pow(f[i], mod - 2, mod)
class Solution:
def makeStringSorted(self, s: str) -> int:
cnt = Counter(s)
ans, n = 0, len(s)
for i, c in enumerate(s):
m = sum(v for a, v in cnt.items() if a < c)
t = f[n - i - 1] * m
for v in cnt.values():
t = t * g[v] % mod
ans = (ans + t) % mod
cnt[c] -= 1
if cnt[c] == 0:
cnt.pop(c)
return ansComplexity
- Time
- O(n × k)
- Space · auxiliary
- O(n)
Pattern: Math and Number Theory
Find the closed form, the invariant, or the modular identity — and skip the loop entirely. LeetCode 1830. Minimum Number of Operations to Make String Sorted is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Math and Combinatorics.
The math and number theory guide has the Python template for the pattern and the 485 LeetCode problems that use it.
Related problems
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|---|---|---|
| 0043 | Multiply Strings | Medium |
| 0168 | Excel Sheet Column Title | Easy |
| 0171 | Excel Sheet Column Number | Easy |
| 0273 | Integer to English Words | Hard |
| 0412 | Fizz Buzz | Easy |
| 0415 | Add Strings | Easy |
Frequently asked questions
- How hard is LeetCode 1830. Minimum Number of Operations to Make String Sorted?
LeetCode 1830. Minimum Number of Operations to Make String Sorted is rated Hard on LeetCode.
- What is the time complexity of LeetCode 1830. Minimum Number of Operations to Make String Sorted?
The Python solution on this page runs in O(n × k).
- What is the space complexity of LeetCode 1830. Minimum Number of Operations to Make String Sorted?
The Python solution on this page uses O(n) auxiliary space.
- What topics does LeetCode 1830. Minimum Number of Operations to Make String Sorted cover?
LeetCode 1830. Minimum Number of Operations to Make String Sorted is tagged Math, String and Combinatorics on LeetCode.