/
missingNumber2.cpp
60 lines (52 loc) · 1.35 KB
/
missingNumber2.cpp
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/**
* Find the missing number in Arithmetic Progression
* Examples:
* Input: arr[] = {2, 4, 8, 10, 12, 14}
* Output: 6
*
* Input: arr[] = {1, 6, 11, 16, 21, 31};
* Output: 26
*/
#include <iostream>
#include <vector>
#include <limits>
int findMissingUtil( std::vector<int> & vec, int diff) {
size_t low = 0;
size_t high = vec.size() - 1;
while ( low < high ) {
size_t mid = ( low + high ) / 2;
//check if the missing element just after mid index is missing.
if ( mid < vec.size() - 1 && vec[mid + 1] - vec[mid] != diff ) {
return vec[mid] + diff;
}
// the element just before mid is missing.
if ( mid > 0 && vec[mid-1] - vec[mid] != diff ) {
return vec[mid - 1] + diff;
}
//the sub array before mid is following AP
if ( vec[mid] == vec[0] + diff * mid ) {
low = mid + 1;
} else {
high = mid - 1;
}
}
return std::numeric_limits<int>::max();
}
void printVec( std::vector<int> & vec ) {
std::cout << "Vec: ";
for ( auto v : vec ) {
std::cout << v << " ";
}
std::cout << std::endl;
}
int missingNumber( std::vector<int> & vec ) {
int diff = (vec[vec.size() - 1] - vec[0])/(vec.size());
return findMissingUtil( vec, diff );
}
int main() {
std::vector<int> vec{ 2, 4, 8, 10, 12, 14 };
printVec(vec);
std::cout << "Missing number in above arithmetic progression is : "
<< missingNumber(vec) << std::endl;
return 0;
}