Arrays
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This C++ function finds a single missing integer in an array by: 1) Calculating the total of all numbers that should be in the full range 2) Summing the numbers in the provided array 3) Returning the difference between the full range total and current array total
![// finds a single missing integer in an array
unsigned Arrays::MissingInt(unsigned* _arr, unsigned _arrSize)
{
// equation for summing all numbers in a range ('- 1' since _arr starts at 1)
unsigned grandTotal = ((_arrSize * (_arrSize + 1)) / 2) - 1;
// summing of numbers in the array
// since array is short by 1, must reduce by 2 to get actual back index value
unsigned front = 0, back = _arrSize - 2, arrTotal = 0;
// two at a time. ie front and back of array (faster)
// do while instead of for loop because i think it looks better (cleaner)
do{
arrTotal += (_arr[front++] + _arr[back--]);
} while (front < back);
// if odd numbered array, front and back will eventually be the same
// need to add ONE of them to arrTotal (not both)
// did this here to avoid running the check every loop
if (front == back) arrTotal += _arr[front];
// subtracting current total from grand total will return the missing number
return grandTotal - arrTotal;
}
// compares values in array to find a single duplicate (multiple versions)
unsigned Arrays::DuplicatedInt(unsigned* _arr, unsigned _arrSize)
{
#if 1
// fast O(count), but extra memory (hash_map)
hash_map<unsigned, unsigned> dupCheck;
for (unsigned count = 0; count < _arrSize; count++)
{
if (!dupCheck.emplace(_arr[count], _arr[count]).second)
return _arr[count];
}
#endif
#if 0
// double for loop = slow O(n^2), but breaks as soon as it finds a duplicate so O(n * count)
// also no extra variable(s)
for (unsigned countA = 0; countA < _arrSize; countA++)
{
for (unsigned countB = countA + 1; countB < _arrSize; countB++)
{
if (_arr[countA] == _arr[countB])
return _arr[countA];
}
}
#endif
#if 0
// takes time to sort (esp w/ 1,000,000 entries), but less memory (no extra variable(s))
O(nlog(n) + count)?
std::sort(_arr, _arr + _arrSize);
for (unsigned count = 0; count < _arrSize; count++)
{
if (_arr[count] == _arr[count + 1])
return _arr[count];
}
#endif
return -1;
}](https://image.slidesharecdn.com/arrays-151023203215-lva1-app6891/85/Arrays-1-320.jpg)
Arrays
- 1. // finds a single missing integer in an array unsigned Arrays::MissingInt(unsigned* _arr, unsigned _arrSize) { // equation for summing all numbers in a range ('- 1' since _arr starts at 1) unsigned grandTotal = ((_arrSize * (_arrSize + 1)) / 2) - 1; // summing of numbers in the array // since array is short by 1, must reduce by 2 to get actual back index value unsigned front = 0, back = _arrSize - 2, arrTotal = 0; // two at a time. ie front and back of array (faster) // do while instead of for loop because i think it looks better (cleaner) do{ arrTotal += (_arr[front++] + _arr[back--]); } while (front < back); // if odd numbered array, front and back will eventually be the same // need to add ONE of them to arrTotal (not both) // did this here to avoid running the check every loop if (front == back) arrTotal += _arr[front]; // subtracting current total from grand total will return the missing number return grandTotal - arrTotal; } // compares values in array to find a single duplicate (multiple versions) unsigned Arrays::DuplicatedInt(unsigned* _arr, unsigned _arrSize) { #if 1 // fast O(count), but extra memory (hash_map) hash_map<unsigned, unsigned> dupCheck; for (unsigned count = 0; count < _arrSize; count++) { if (!dupCheck.emplace(_arr[count], _arr[count]).second) return _arr[count]; } #endif #if 0 // double for loop = slow O(n^2), but breaks as soon as it finds a duplicate so O(n * count) // also no extra variable(s) for (unsigned countA = 0; countA < _arrSize; countA++) { for (unsigned countB = countA + 1; countB < _arrSize; countB++) { if (_arr[countA] == _arr[countB]) return _arr[countA]; } } #endif #if 0 // takes time to sort (esp w/ 1,000,000 entries), but less memory (no extra variable(s)) O(nlog(n) + count)? std::sort(_arr, _arr + _arrSize); for (unsigned count = 0; count < _arrSize; count++) { if (_arr[count] == _arr[count + 1]) return _arr[count]; } #endif return -1; }