STL-------------partial_sum
STL http://www.cplusplus.com/reference/algorithm/count/ template <class InputIterator, class OutputIterator>
OutputIterator partial_sum ( InputIterator first, InputIterator last,
OutputIterator result );
template <class InputIterator, class OutputIterator, class BinaryOperation>
OutputIterator partial_sum ( InputIterator first, InputIterator last,
OutputIterator result, BinaryOperation binary_op );
Compute partial sums of range
Assigns to every element in the range starting at
result the partial sum of the corresponding elements in the range [first,last).
If
x represents an element in [first,last) and
y represents an element in
result, the
ys can be calculated as:
y
0 = x
0
y
1 = x
0 + x
1
y
2 = x
0 + x
1 + x
2
y
3 = x
0 + x
1 + x
2 + x
3
y
4 = x
0 + x
1 + x
2 + x
3 + x
4
... ... ...
The default operation is to add the elements up, but a different operation can be specified as
binary_op instead.
The behavior of this function template is equivalent to:
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template <class InputIterator, class OutputIterator>
OutputIterator partial_sum ( InputIterator first, InputIterator last,
OutputIterator result )
{
iterator_traits<InputIterator>::value_type val;
*result++ = val = *first++;
while (first!=last)
*result++ = val = val + *first++;
// or: *result++ = val = binary_op(val,*first++) for binary_op version
return result;
}Parameters
first, last
Input iterators to the initial and final positions in a sequence. The range used is [first,last), which contains all the elements between
first and
last, including the element pointed by
first but not the element pointed by
last.
result
Output iterator to the initial position in the destination sequence where the partial sums are stored. The range starts at
result and shall have a size large enough to contain as many elements as the range above ( [first,last)).
binary_op
Binary operation taking as arguments two elements of the type pointed by the
InputIterator, and returning the result of the replacement for the sum operation. This can either be a pointer to a function or an object whose class overloads operator().
Return value An iterator pointing to past the last element of the destination sequence where resulting elements have been stored.
Example
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// partial_sum example
#include <iostream>
#include <functional>
#include <numeric>
using namespace std;
int myop (int x, int y) {return x+y+1;}
int main () {
int val[] = {1,2,3,4,5};
int result[5];
partial_sum (val, val+5, result);
cout << "using default partial_sum: ";
for (int i=0; i<5; i++) cout << result[i] << ' ';
cout << endl;
partial_sum (val, val+5, result, multiplies<int>());
cout << "using functional operation multiplies: ";
for (int i=0; i<5; i++) cout << result[i] << ' ';
cout << endl;
partial_sum (val, val+5, result, myop);
cout << "using custom function: ";
for (int i=0; i<5; i++) cout << result[i] << ' ';
cout << endl;
return 0;
}#include
int myop (int x, int y) {return x+y+1;}
int main () { int val[] = {1,2,3,4,5}; int result[5];
partial_sum (val, val+5, result); cout << "using default partial_sum: "; for (int i=0; i<5; i++) cout << result[i] << ' '; cout << endl;
partial_sum (val, val+5, result, multiplies
partial_sum (val, val+5, result, myop); cout << "using custom function: "; for (int i=0; i<5; i++) cout << result[i] << ' '; cout << endl; return 0; }
Output:
using default partial_sum: 1 3 6 10 15
using functional operation multiplies: 1 2 6 24 120
using custom function: 1 4 8 13 19
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