如果要想真正学好STL 提供网站 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:
y0 = x0
y1 = x0 + x1
y2 = x0 + x1 + x2
y3 = x0 + x1 + x2 + x3
y4 = x0 + x1 + x2 + x3 + x4
... ... ...
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:
| |
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
| |
#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;
}
Output:
|