1 | |
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2 | /// `MinMaxResult` is an enum returned by `minmax`. |

3 | /// |

4 | /// See [`.minmax()`](crate::Itertools::minmax) for more detail. |

5 | #[derive(Copy, Clone, PartialEq, Debug)] |

6 | pub enum MinMaxResult<T> { |

7 | /// Empty iterator |

8 | NoElements, |

9 | |

10 | /// Iterator with one element, so the minimum and maximum are the same |

11 | OneElement(T), |

12 | |

13 | /// More than one element in the iterator, the first element is not larger |

14 | /// than the second |

15 | MinMax(T, T) |

16 | } |

17 | |

18 | impl<T: Clone> MinMaxResult<T> { |

19 | /// `into_option` creates an `Option` of type `(T, T)`. The returned `Option` |

20 | /// has variant `None` if and only if the `MinMaxResult` has variant |

21 | /// `NoElements`. Otherwise `Some((x, y))` is returned where `x <= y`. |

22 | /// If the `MinMaxResult` has variant `OneElement(x)`, performing this |

23 | /// operation will make one clone of `x`. |

24 | /// |

25 | /// # Examples |

26 | /// |

27 | /// ``` |

28 | /// use itertools::MinMaxResult::{self, NoElements, OneElement, MinMax}; |

29 | /// |

30 | /// let r: MinMaxResult<i32> = NoElements; |

31 | /// assert_eq!(r.into_option(), None); |

32 | /// |

33 | /// let r = OneElement(1); |

34 | /// assert_eq!(r.into_option(), Some((1, 1))); |

35 | /// |

36 | /// let r = MinMax(1, 2); |

37 | /// assert_eq!(r.into_option(), Some((1, 2))); |

38 | /// ``` |

39 | pub fn into_option(self) -> Option<(T,T)> { |

40 | match self { |

41 | MinMaxResult::NoElements => None, |

42 | MinMaxResult::OneElement(x) => Some((x.clone(), x)), |

43 | MinMaxResult::MinMax(x, y) => Some((x, y)) |

44 | } |

45 | } |

46 | } |

47 | |

48 | /// Implementation guts for `minmax` and `minmax_by_key`. |

49 | pub fn minmax_impl<I, K, F, L>(mut it: I, mut key_for: F, |

50 | mut lt: L) -> MinMaxResult<I::Item> |

51 | where I: Iterator, |

52 | F: FnMut(&I::Item) -> K, |

53 | L: FnMut(&I::Item, &I::Item, &K, &K) -> bool, |

54 | { |

55 | let (mut min, mut max, mut min_key, mut max_key) = match it.next() { |

56 | None => return MinMaxResult::NoElements, |

57 | Some(x) => { |

58 | match it.next() { |

59 | None => return MinMaxResult::OneElement(x), |

60 | Some(y) => { |

61 | let xk = key_for(&x); |

62 | let yk = key_for(&y); |

63 | if !lt(&y, &x, &yk, &xk) {(x, y, xk, yk)} else {(y, x, yk, xk)} |

64 | } |

65 | } |

66 | } |

67 | }; |

68 | |

69 | loop { |

70 | // `first` and `second` are the two next elements we want to look |

71 | // at. We first compare `first` and `second` (#1). The smaller one |

72 | // is then compared to current minimum (#2). The larger one is |

73 | // compared to current maximum (#3). This way we do 3 comparisons |

74 | // for 2 elements. |

75 | let first = match it.next() { |

76 | None => break, |

77 | Some(x) => x |

78 | }; |

79 | let second = match it.next() { |

80 | None => { |

81 | let first_key = key_for(&first); |

82 | if lt(&first, &min, &first_key, &min_key) { |

83 | min = first; |

84 | } else if !lt(&first, &max, &first_key, &max_key) { |

85 | max = first; |

86 | } |

87 | break; |

88 | } |

89 | Some(x) => x |

90 | }; |

91 | let first_key = key_for(&first); |

92 | let second_key = key_for(&second); |

93 | if !lt(&second, &first, &second_key, &first_key) { |

94 | if lt(&first, &min, &first_key, &min_key) { |

95 | min = first; |

96 | min_key = first_key; |

97 | } |

98 | if !lt(&second, &max, &second_key, &max_key) { |

99 | max = second; |

100 | max_key = second_key; |

101 | } |

102 | } else { |

103 | if lt(&second, &min, &second_key, &min_key) { |

104 | min = second; |

105 | min_key = second_key; |

106 | } |

107 | if !lt(&first, &max, &first_key, &max_key) { |

108 | max = first; |

109 | max_key = first_key; |

110 | } |

111 | } |

112 | } |

113 | |

114 | MinMaxResult::MinMax(min, max) |

115 | } |

116 |