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Difference between revisions of "cpp/algorithm/mismatch"

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Revision as of 21:45, 31 May 2013

 
C++
 
Algorithm library
Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
Non-modifying sequence operations
Batch operations
(C++17)
Search operations
(C++11)                (C++11)(C++11)
mismatch

Modifying sequence operations
Copy operations
(C++11)
(C++11)
(C++11)
Swap operations
Transformation operations
Generation operations
Removing operations
Order-changing operations
(until C++17)(C++11)
(C++20)(C++20)
Sampling operations
(C++17)

Sorting and related operations
Partitioning operations
Sorting operations
Binary search operations
(on partitioned ranges)
Set operations (on sorted ranges)
Merge operations (on sorted ranges)
Heap operations
Minimum/maximum operations
(C++11)
(C++17)
Lexicographical comparison operations
(C++20)
Permutation operations
C library
Numeric operations
Operations on uninitialized memory
 
Defined in header <algorithm>
template< class InputIt1, class InputIt2 >

std::pair<InputIt1,InputIt2>
    mismatch( InputIt1 first1, InputIt1 last1,

              InputIt2 first2 );
 (1)
template< class InputIt1, class InputIt2, class BinaryPredicate >

std::pair<InputIt1,InputIt2>
    mismatch( InputIt1 first1, InputIt1 last1,
              InputIt2 first2,

              BinaryPredicate p );
 (2)
template< class InputIt1, class InputIt2 >

std::pair<InputIt1,InputIt2>
    mismatch( InputIt1 first1, InputIt1 last1,

              InputIt2 first2, InputIt2 last2 );
 (3) (since C++14)
template< class InputIt1, class InputIt2, class BinaryPredicate >

std::pair<InputIt1,InputIt2>
    mismatch( InputIt1 first1, InputIt1 last1,
              InputIt2 first2, InputIt2 last2,

              BinaryPredicate p );
 (4) (since C++14)

Returns the first mismatching pair of elements from two ranges: one defined by [first1, last1) and another defined by [first2,last2). If last2 is not provided (overloads (1) and (2)), it denotes first2 + (last1 - first1).

Overloads (1) and (3) use operator== to compare the elements, the overloads (2) and (4) use the given binary predicate p.

Contents

Parameters

first1, last1 - the first range of the elements
first2, last2 - the second range of the elements
p - binary predicate which returns ​true if the elements should be treated as equal.

The signature of the predicate function should be equivalent to the following:

 bool pred(const Type1 &a, const Type2 &b);

While the signature does not need to have const &, the function must not modify the objects passed to it and must be able to accept all values of type (possibly const) Type1 and Type2 regardless of value category (thus, Type1 & is not allowed, nor is Type1 unless for Type1 a move is equivalent to a copy(since C++11)).
The types Type1 and Type2 must be such that objects of types InputIt1 and InputIt2 can be dereferenced and then implicitly converted to Type1 and Type2 respectively. ​

Type requirements

Template:par req concept Template:par req concept Template:par req concept

Return value

std::pair with iterators to the first two non-equivalent elements.

If no mismatches are found when the comparison reaches last1, the pair holds last1 and the corresponding iterator from the second range. The behavior is undefined if the second range is shorter than the first range. (until C++14)
If no mismatches are found when the comparison reaches last1 or last2, whichever happens first, the pair holds the end iterator and the corresponding iterator from the other range. (since C++14)

Complexity

At most last1 - first1 applications of the predicate

Possible implementation

First version 
template<class InputIt1, class InputIt2>
std::pair<InputIt1, InputIt2>
    mismatch(InputIt1 first1, InputIt1 last1, InputIt2 first2)
{
    while (first1 != last1 && *first1 == *first2) {
        ++first1, ++first2;
    }
    return std::make_pair(first1, first2);
}
Second version 
template<class InputIt1, class InputIt2, class BinaryPredicate>
std::pair<InputIt1, InputIt2>
    mismatch(InputIt1 first1, InputIt1 last1, InputIt2 first2, BinaryPredicate p)
{
    while (first1 != last1 && p(*first1, *first2)) {
        ++first1, ++first2;
    }
    return std::make_pair(first1, first2);
}

Example

This program determines the longest substring that is simultaneously found at the very beginning of the given string and at the very end of it, in reverse order (possibly overlapping)

Run this code
#include <iostream>
#include <string>
#include <algorithm>
 
std::string mirror_ends(const std::string& in)
{
    return std::string(in.begin(),
                       std::mismatch(in.begin(), in.end(), in.rbegin()).first);
}
 
int main()
{
    std::cout << mirror_ends("abXYZba") << '\n'
              << mirror_ends("abca") << '\n'
              << mirror_ends("aba") << '\n';
}

Output: 

ab
a
aba

See also

 determines if two sets of elements are the same
(function template) [edit]
(C++11)
 finds the first element satisfying specific criteria
(function template) [edit]
returns true if one range is lexicographically less than another
(function template) [edit]
searches for the first occurrence of a range of elements
(function template) [edit]
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