Minimum Number of Operations to Make Array Continuous LeetCode solution in C++

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// OJ:
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// https://leetcode.com/problems/minimum-number-of-operations-to-make-array-continuous/
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// Author: github.com/lzl124631x
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// Time: O(NlogN)
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// Space: O(1)
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class Solution {
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 public:
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  int minOperations(vector<int> &A) {
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    int N = A.size(), ans = N, j = 0;
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    sort(begin(A), end(A));
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    A.erase(unique(begin(A), end(A)), end(A)); // only keep unique elements
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    int M = A.size();
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    for (int i = 0; i < M; ++i) {
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      while (j < M && A[j] < A[i] + N)
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        ++j; // let `j` point to the first element that is out of range -- `>=
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             // A[i] + N`.
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      ans = min(ans,
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                N - j + i); // The length of this subarray is `j - i`. We need to
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                            // replace `N - j + i` elements to make it continuous.
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    }
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    return ans;
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  }
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};