Determine if A is permutation of B using ASCII values

Question

I wrote an function to determine if string a is a permutation of string b. The definition is as follows:

bool isPermutation(std::string         


        

Answer 1

std::sort( strOne.begin(), strOne.end() );
std::sort( strTwo.begin(), strTwo.end() );    
return strOne == strTwo;

will be sufficient.

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My suggestion is to use std::unordered_map

i.e.

std::unordered_map< char, unsigned > umapOne;
std::unordered_map< char, unsigned > umapTwo;
for( char c : strOne ) ++umapOne[c];
for( char c : strTwo ) ++umapTwo[c];
return umapOne == umapTwo;

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As an optimization you can add at the top for a solution

if( strOne.size() != strTwo.size() ) return false;

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Better std::unordered_map solution,

if( strOne.size() != strTwo.size() ) return false; // required
std::unordered_map< char, int > umap;
for( char c : strOne ) ++umap[c];
for( char c : strTwo ) if( --umap[c] < 0 )  return false;
return true;

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If you need to just solve a problem without knowing how to do it, you may use std::is_permutation

return std::is_permutation( strOne.begin(), strOne.end(), strTwo.begin(), strTwo.end() );