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Faster minmax by using fold #968

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Faster minmax by using fold #968

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69 changes: 33 additions & 36 deletions src/minmax.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -67,48 +67,45 @@ where
},
};

loop {
// `first` and `second` are the two next elements we want to look
// at. We first compare `first` and `second` (#1). The smaller one
// is then compared to current minimum (#2). The larger one is
// compared to current maximum (#3). This way we do 3 comparisons
// for 2 elements.
let first = match it.next() {
None => break,
Some(x) => x,
};
let second = match it.next() {
None => {
let first_key = key_for(&first);
let remaining = it.fold(None, |acc, second| match acc {
None => Some(second),
Some(first) => {
// `first` and `second` are the two next elements we want to look
// at. We first compare `first` and `second` (#1). The smaller one
// is then compared to current minimum (#2). The larger one is
// compared to current maximum (#3). This way we do 3 comparisons
// for 2 elements.
let first_key = key_for(&first);
let second_key = key_for(&second);
if !lt(&second, &first, &second_key, &first_key) {
if lt(&first, &min, &first_key, &min_key) {
min = first;
} else if !lt(&first, &max, &first_key, &max_key) {
min_key = first_key;
}
if !lt(&second, &max, &second_key, &max_key) {
max = second;
max_key = second_key;
}
} else {
if lt(&second, &min, &second_key, &min_key) {
min = second;
min_key = second_key;
}
if !lt(&first, &max, &first_key, &max_key) {
max = first;
max_key = first_key;
}
break;
}
Some(x) => x,
};
None
}
});

if let Some(first) = remaining {
let first_key = key_for(&first);
let second_key = key_for(&second);
if !lt(&second, &first, &second_key, &first_key) {
if lt(&first, &min, &first_key, &min_key) {
min = first;
min_key = first_key;
}
if !lt(&second, &max, &second_key, &max_key) {
max = second;
max_key = second_key;
}
} else {
if lt(&second, &min, &second_key, &min_key) {
min = second;
min_key = second_key;
}
if !lt(&first, &max, &first_key, &max_key) {
max = first;
max_key = first_key;
}
if lt(&first, &min, &first_key, &min_key) {
min = first;
} else if !lt(&first, &max, &first_key, &max_key) {
max = first;
}
}

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