cpp/algorithm/count

Returns the number of elements in the range satisfying specific criteria. @1@ counts the elements that are equal to (using ). @3@ counts elements for which predicate returns. @2,4@ Same as, but executed according to.

Return value
The number of iterators in the range  satisfying the following condition: @1,2@ is @3,4@  is

Complexity
Given as : @1,2@ exactly comparisons with  using @3,4@ exactly applications of the predicate

Possible implementation
See also the implementations of in libstdc++ and libc++.

See also the implementations of in libstdc++ and libc++.