Use STL algorithms available since C++14 to implement container

algorithms (when possible).

Prior to C++14, many STL container algorithms required size checks
because because the second container only used one iterator as an
input. This is not an issue for some algorithms since C++14 added
two iterator versions.

PiperOrigin-RevId: 575296640
Change-Id: I9e4fc8c75cba7cdb0cde10bdd7c5c75e07f414ae

absl/algorithm/container.h

@@ -116,18 +116,6 @@ template <class Key, class Hash, class KeyEqual, class Allocator>
 struct IsUnorderedContainer<std::unordered_set<Key, Hash, KeyEqual, Allocator>>
     : std::true_type {};
 
-// container_algorithm_internal::c_size. It is meant for internal use only.
-
-template <class C>
-auto c_size(C& c) -> decltype(c.size()) {
-  return c.size();
-}
-
-template <class T, std::size_t N>
-constexpr std::size_t c_size(T (&)[N]) {
-  return N;
-}
-
 }  // namespace container_algorithm_internal
 
 // PUBLIC API
@@ -348,20 +336,10 @@ container_algorithm_internal::ContainerDifferenceType<const C> c_count_if(
 template <typename C1, typename C2>
 container_algorithm_internal::ContainerIterPairType<C1, C2> c_mismatch(C1& c1,
                                                                        C2& c2) {
-  auto first1 = container_algorithm_internal::c_begin(c1);
-  auto last1 = container_algorithm_internal::c_end(c1);
-  auto first2 = container_algorithm_internal::c_begin(c2);
-  auto last2 = container_algorithm_internal::c_end(c2);
-
-  for (; first1 != last1 && first2 != last2; ++first1, (void)++first2) {
-    // Negates equality because Cpp17EqualityComparable doesn't require clients
-    // to overload both `operator==` and `operator!=`.
-    if (!(*first1 == *first2)) {
-      break;
-    }
-  }
-
-  return std::make_pair(first1, first2);
+  return std::mismatch(container_algorithm_internal::c_begin(c1),
+                       container_algorithm_internal::c_end(c1),
+                       container_algorithm_internal::c_begin(c2),
+                       container_algorithm_internal::c_end(c2));
 }
 
 // Overload of c_mismatch() for using a predicate evaluation other than `==` as
@@ -370,56 +348,33 @@ container_algorithm_internal::ContainerIterPairType<C1, C2> c_mismatch(C1& c1,
 template <typename C1, typename C2, typename BinaryPredicate>
 container_algorithm_internal::ContainerIterPairType<C1, C2> c_mismatch(
     C1& c1, C2& c2, BinaryPredicate pred) {
-  auto first1 = container_algorithm_internal::c_begin(c1);
-  auto last1 = container_algorithm_internal::c_end(c1);
-  auto first2 = container_algorithm_internal::c_begin(c2);
-  auto last2 = container_algorithm_internal::c_end(c2);
-
-  for (; first1 != last1 && first2 != last2; ++first1, (void)++first2) {
-    if (!pred(*first1, *first2)) {
-      break;
-    }
-  }
-
-  return std::make_pair(first1, first2);
+  return std::mismatch(container_algorithm_internal::c_begin(c1),
+                       container_algorithm_internal::c_end(c1),
+                       container_algorithm_internal::c_begin(c2),
+                       container_algorithm_internal::c_end(c2), pred);
 }
 
 // c_equal()
 //
 // Container-based version of the <algorithm> `std::equal()` function to
 // test whether two containers are equal.
-//
-// NOTE: the semantics of c_equal() are slightly different than those of
-// equal(): while the latter iterates over the second container only up to the
-// size of the first container, c_equal() also checks whether the container
-// sizes are equal.  This better matches expectations about c_equal() based on
-// its signature.
-//
-// Example:
-//   vector v1 = <1, 2, 3>;
-//   vector v2 = <1, 2, 3, 4>;
-//   equal(std::begin(v1), std::end(v1), std::begin(v2)) returns true
-//   c_equal(v1, v2) returns false
-
 template <typename C1, typename C2>
 bool c_equal(const C1& c1, const C2& c2) {
-  return ((container_algorithm_internal::c_size(c1) ==
-           container_algorithm_internal::c_size(c2)) &&
-          std::equal(container_algorithm_internal::c_begin(c1),
-                     container_algorithm_internal::c_end(c1),
-                     container_algorithm_internal::c_begin(c2)));
+  return std::equal(container_algorithm_internal::c_begin(c1),
+                    container_algorithm_internal::c_end(c1),
+                    container_algorithm_internal::c_begin(c2),
+                    container_algorithm_internal::c_end(c2));
 }
 
 // Overload of c_equal() for using a predicate evaluation other than `==` as
 // the function's test condition.
 template <typename C1, typename C2, typename BinaryPredicate>
 bool c_equal(const C1& c1, const C2& c2, BinaryPredicate&& pred) {
-  return ((container_algorithm_internal::c_size(c1) ==
-           container_algorithm_internal::c_size(c2)) &&
-          std::equal(container_algorithm_internal::c_begin(c1),
-                     container_algorithm_internal::c_end(c1),
-                     container_algorithm_internal::c_begin(c2),
-                     std::forward<BinaryPredicate>(pred)));
+  return std::equal(container_algorithm_internal::c_begin(c1),
+                    container_algorithm_internal::c_end(c1),
+                    container_algorithm_internal::c_begin(c2),
+                    container_algorithm_internal::c_end(c2),
+                    std::forward<BinaryPredicate>(pred));
 }
 
 // c_is_permutation()
@@ -428,20 +383,20 @@ bool c_equal(const C1& c1, const C2& c2, BinaryPredicate&& pred) {
 // to test whether a container is a permutation of another.
 template <typename C1, typename C2>
 bool c_is_permutation(const C1& c1, const C2& c2) {
-  using std::begin;
-  using std::end;
-  return c1.size() == c2.size() &&
-         std::is_permutation(begin(c1), end(c1), begin(c2));
+  return std::is_permutation(container_algorithm_internal::c_begin(c1),
+                             container_algorithm_internal::c_end(c1),
+                             container_algorithm_internal::c_begin(c2),
+                             container_algorithm_internal::c_end(c2));
 }
 
 // Overload of c_is_permutation() for using a predicate evaluation other than
 // `==` as the function's test condition.
 template <typename C1, typename C2, typename BinaryPredicate>
 bool c_is_permutation(const C1& c1, const C2& c2, BinaryPredicate&& pred) {
-  using std::begin;
-  using std::end;
-  return c1.size() == c2.size() &&
-         std::is_permutation(begin(c1), end(c1), begin(c2),
+  return std::is_permutation(container_algorithm_internal::c_begin(c1),
+                             container_algorithm_internal::c_end(c1),
+                             container_algorithm_internal::c_begin(c2),
+                             container_algorithm_internal::c_end(c2),
                              std::forward<BinaryPredicate>(pred));
 }