CS253: Software Development with C++

Spring 2018

Sort Algorithm

See this page as a slide show

CS253 Sort Algorithm

The sort algorithm

The sort algorithm (from the header file <algorithm>) has two forms:

Containers

Default comparison

string s = "Kokopelli";
sort(s.begin(), s.end());
cout << s << '\n';
Keiklloop

Explicit comparison

string s = "Kokopelli";
sort(s.begin(), s.end(), less<char>);
cout << s << '\n';
c.cc: In function 'int main()':
c.cc:2:36: error: expected primary-expression before ')' token

Explicit comparison

string s = "Kokopelli";
sort(s.begin(), s.end(), less<char>());
cout << s << '\n';
Keiklloop

Reverse sort

string s = "Kokopelli";
sort(s.begin(), s.end(), greater<char>());
cout << s << '\n';
poollkieK

Comparison function

bool lt(char a, char b) {
    return a < b;
}

int main() {
    string s = "Kokopelli";
    sort(s.begin(), s.end(), lt);
    cout << s << '\n';
}
Keiklloop

λ-function

string s = "Kokopelli";
sort(s.begin(), s.end(),
     [](char a, char b){return a<b;});
cout << s << '\n';
Keiklloop

Case folding

bool lt(char a, char b) {
    return toupper(a) < toupper(b);
}

int main() {
    string s = "Kokopelli";
    sort(s.begin(), s.end(), lt);
    cout << s << '\n';
}
eiKklloop

Unique

If you want to avoid duplicates, then use unique.

bool lt(char a, char b) {
    return toupper(a) < toupper(b);
}

int main() {
    string s = "Kokopelli";
    sort(s.begin(), s.end(), lt);
    auto it = unique(s.begin(), s.end());
    s.resize(it-s.begin());
    cout << s << '\n';
}
eiKklop

unique assumes that its input is in order already.

Unique

Case-independent uniqueness doesn’t come free:

bool lt(char a, char b) {
    return toupper(a) < toupper(b);
}

bool eq(char a, char b) {
    return toupper(a) == toupper(b);
}

int main() {
    string s = "Kokopelli";
    sort(s.begin(), s.end(), lt);
    auto it = unique(s.begin(), s.end(), eq);
    s.resize(it-s.begin());
    cout << s << '\n';
}
eiKlop

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Modified: 2018-04-24T16:55

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