PermMissingElem

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problem

solution

option 1 - XOR

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// you can use includes, for example:
// #include <algorithm>

// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;

int solution(vector<int> &A) {
    // write your code in C++14 (g++ 6.2.0)
    int n = A.size(), ret = n+1;
    for(int i=0;i<n;++i) ret^= ((i+1)^A[i]);
    return ret;
}

option 2

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// you can use includes, for example:
// #include <algorithm>

// you can write to stdout for debugging purposes, e.g.
// cout << "this is a debug message" << endl;

int solution(vector<int> &A) {
    // write your code in C++14 (g++ 6.2.0)
    int n = A.size(), total = n+1;
    for(int i=0;i<n;++i) total+=(i+1-A[i]);
    return total;
}

analysis

  • time complexity O(n)
  • space complexity O(1)