product except self Algorithm
In euclidean geometry, the dot merchandise of the Cartesian coordinates of two vectors is widely used and often named" the" inner merchandise (or rarely projection merchandise) of euclidean space even though it is not the only inner merchandise that can be specify on euclidean space; see also inner merchandise space.the cosine of the angle of two vectors is the quotient of their dot merchandise by the merchandise of their lengths).
/*
* Given an array of n integers where n > 1, nums, return an array output
* such that output[i] is equal to the product of all the elements of nums except nums[i].
* Example: [1, 2, 3, 4] ==> [24, 12, 8, 6]
*
* Try to use constant space. (excluding result array)
*/
#include <iostream>
#include <vector>
/*
* Idea is to maintain two product variables, one from beginning and
* one from the end.
* Each result variable in result array
* would be touched twice, one from the left to right
* and other right to left, thus producing desired result.
*/
std::vector<int> product_except_self(const std::vector<int>& nums)
{
int product_from_beginning = 1;
int product_from_end = 1;
unsigned int n = nums.size();
std::vector<int> result(n, 1);
for (unsigned int i = 0; i < n; ++i) {
result[i] *= product_from_beginning;
product_from_beginning *= nums[i];
result[n-1-i] *= product_from_end;
product_from_end *= nums[n-1-i];
}
return result;
}
void print_vector(const std::vector<int>& vec)
{
for (auto n : vec) {
std::cout << n << " ";
}
std::cout << std::endl;
}
int main()
{
std::vector<int> vec{1, 2, 3, 4};
std::cout << "Input Vector: ";
print_vector(vec);
std::vector<int> result = product_except_self(vec);
std::cout << "Output Vector: ";
print_vector(result);
}
