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Change compareFn to fn (a: T, b: T) std.math.Order

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Zander Khan 2021-01-18 19:02:11 +00:00
parent 5bfd9238de
commit ce22c70586
2 changed files with 98 additions and 72 deletions
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129
lib/std/priority_dequeue.zig
View file

@ -7,6 +7,7 @@ const std = @import("std.zig");
const Allocator = std.mem.Allocator;
const assert = std.debug.assert;
const warn = std.debug.warn;
const Order = std.math.Order;
const testing = std.testing;
const expect = testing.expect;
const expectEqual = testing.expectEqual;
@ -20,31 +21,26 @@ pub fn PriorityDequeue(comptime T: type) type {
items: []T,
len: usize,
allocator: *Allocator,
lessThanFn: fn (a: T, b: T) bool,
compareFn: fn (a: T, b: T) Order,
/// Initialize and return a new dequeue. Provide `lessThanFn`
/// that returns `true` when its first argument should
/// get min-popped before its second argument. For example,
/// to make `popMin` return the minimum value, provide
/// Initialize and return a new priority dequeue. Provide `compareFn`
/// that returns `Order.lt` when its first argument should
/// get min-popped before its second argument, `Order.eq` if the
/// arguments are of equal priority, or `Order.gt` if the second
/// argument should be min-popped first. Popping the max element works
/// in reverse. For example, to make `popMin` return the smallest
/// number, provide
///
/// `fn lessThanFn(a: T, b: T) bool { return a < b; }`
pub fn init(allocator: *Allocator, lessThanFn: fn (T, T) bool) Self {
/// `fn lessThan(a: T, b: T) Order { return std.math.order(a, b); }`
pub fn init(allocator: *Allocator, compareFn: fn (T, T) Order) Self {
return Self{
.items = &[_]T{},
.len = 0,
.allocator = allocator,
.lessThanFn = lessThanFn,
.compareFn = compareFn,
};
}
fn lessThan(self: Self, a: T, b: T) bool {
return self.lessThanFn(a, b);
}
fn greaterThan(self: Self, a: T, b: T) bool {
return self.lessThanFn(b, a);
}
/// Free memory used by the dequeue.
pub fn deinit(self: Self) void {
self.allocator.free(self.items);
@ -100,7 +96,8 @@ pub fn PriorityDequeue(comptime T: type) type {
const parent = self.items[parent_index];
const min_layer = self.nextIsMinLayer();
if ((min_layer and self.greaterThan(child, parent)) or (!min_layer and self.lessThan(child, parent))) {
const order = self.compareFn(child, parent);
if ((min_layer and order == .gt) or (!min_layer and order == .lt)) {
// We must swap the item with it's parent if it is on the "wrong" layer
self.items[parent_index] = child;
self.items[child_index] = parent;
@ -118,21 +115,21 @@ pub fn PriorityDequeue(comptime T: type) type {
fn siftUp(self: *Self, start: StartIndexAndLayer) void {
if (start.min_layer) {
doSiftUp(self, start.index, lessThan);
doSiftUp(self, start.index, .lt);
} else {
doSiftUp(self, start.index, greaterThan);
doSiftUp(self, start.index, .gt);
}
}
fn doSiftUp(self: *Self, start_index: usize, compare: fn (Self, T, T) bool) void {
fn doSiftUp(self: *Self, start_index: usize, target_order: Order) void {
var child_index = start_index;
while (child_index > 2) {
var grandparent_index = grandparentIndex(child_index);
const child = self.items[child_index];
const grandparent = self.items[grandparent_index];
// If the grandparent is already better, we have gone as far as we need to
if (!compare(self.*, child, grandparent)) break;
// If the grandparent is already better or equal, we have gone as far as we need to
if (self.compareFn(child, grandparent) != target_order) break;
// Otherwise swap the item with it's grandparent
self.items[grandparent_index] = child;
@ -153,14 +150,14 @@ pub fn PriorityDequeue(comptime T: type) type {
if (self.len == 0) return null;
if (self.len == 1) return self.items[0];
if (self.len == 2) return self.items[1];
return self.bestItemAtIndices(1, 2, greaterThan).item;
return self.bestItemAtIndices(1, 2, .gt).item;
}
fn maxIndex(self: Self) ?usize {
if (self.len == 0) return null;
if (self.len == 1) return 0;
if (self.len == 2) return 1;
return self.bestItemAtIndices(1, 2, greaterThan).index;
return self.bestItemAtIndices(1, 2, .gt).index;
}
/// Pop the smallest element from the dequeue. Returns
@ -204,13 +201,13 @@ pub fn PriorityDequeue(comptime T: type) type {
fn siftDown(self: *Self, index: usize) void {
if (isMinLayer(index)) {
self.doSiftDown(index, lessThan);
self.doSiftDown(index, .lt);
} else {
self.doSiftDown(index, greaterThan);
self.doSiftDown(index, .gt);
}
}
fn doSiftDown(self: *Self, start_index: usize, compare: fn (Self, T, T) bool) void {
fn doSiftDown(self: *Self, start_index: usize, target_order: Order) void {
var index = start_index;
const half = self.len >> 1;
while (true) {
@ -225,12 +222,12 @@ pub fn PriorityDequeue(comptime T: type) type {
const index3 = index2 + 1;
// Find the best grandchild
const best_left = self.bestItemAtIndices(first_grandchild_index, index2, compare);
const best_right = self.bestItemAtIndices(index3, last_grandchild_index, compare);
const best_grandchild = self.bestItem(best_left, best_right, compare);
const best_left = self.bestItemAtIndices(first_grandchild_index, index2, target_order);
const best_right = self.bestItemAtIndices(index3, last_grandchild_index, target_order);
const best_grandchild = self.bestItem(best_left, best_right, target_order);
// If the item is better than it's best grandchild, we are done
if (compare(self.*, elem, best_grandchild.item) or elem == best_grandchild.item) return;
// If the item is better than or equal to its best grandchild, we are done
if (self.compareFn(best_grandchild.item, elem) != target_order) return;
// Otherwise, swap them
self.items[best_grandchild.index] = elem;
@ -238,16 +235,16 @@ pub fn PriorityDequeue(comptime T: type) type {
index = best_grandchild.index;
// We might need to swap the element with it's parent
self.swapIfParentIsBetter(elem, index, compare);
self.swapIfParentIsBetter(elem, index, target_order);
} else {
// The children or grandchildren are the last layer
const first_child_index = firstChildIndex(index);
if (first_child_index > self.len) return;
const best_descendent = self.bestDescendent(first_child_index, first_grandchild_index, compare);
const best_descendent = self.bestDescendent(first_child_index, first_grandchild_index, target_order);
// If the best descendant is still larger, we are done
if (compare(self.*, elem, best_descendent.item) or elem == best_descendent.item) return;
// If the item is better than or equal to its best descendant, we are done
if (self.compareFn(best_descendent.item, elem) != target_order) return;
// Otherwise swap them
self.items[best_descendent.index] = elem;
@ -258,7 +255,7 @@ pub fn PriorityDequeue(comptime T: type) type {
if (index < first_grandchild_index) return;
// We might need to swap the element with it's parent
self.swapIfParentIsBetter(elem, index, compare);
self.swapIfParentIsBetter(elem, index, target_order);
return;
}
@ -267,11 +264,11 @@ pub fn PriorityDequeue(comptime T: type) type {
}
}
fn swapIfParentIsBetter(self: *Self, child: T, child_index: usize, compare: fn (Self, T, T) bool) void {
fn swapIfParentIsBetter(self: *Self, child: T, child_index: usize, target_order: Order) void {
const parent_index = parentIndex(child_index);
const parent = self.items[parent_index];
if (compare(self.*, parent, child)) {
if (self.compareFn(parent, child) == target_order) {
self.items[parent_index] = child;
self.items[child_index] = parent;
}
@ -289,21 +286,21 @@ pub fn PriorityDequeue(comptime T: type) type {
};
}
fn bestItem(self: Self, item1: ItemAndIndex, item2: ItemAndIndex, compare: fn (Self, T, T) bool) ItemAndIndex {
if (compare(self, item1.item, item2.item)) {
fn bestItem(self: Self, item1: ItemAndIndex, item2: ItemAndIndex, target_order: Order) ItemAndIndex {
if (self.compareFn(item1.item, item2.item) == target_order) {
return item1;
} else {
return item2;
}
}
fn bestItemAtIndices(self: Self, index1: usize, index2: usize, compare: fn (Self, T, T) bool) ItemAndIndex {
fn bestItemAtIndices(self: Self, index1: usize, index2: usize, target_order: Order) ItemAndIndex {
var item1 = self.getItem(index1);
var item2 = self.getItem(index2);
return self.bestItem(item1, item2, compare);
return self.bestItem(item1, item2, target_order);
}
fn bestDescendent(self: Self, first_child_index: usize, first_grandchild_index: usize, compare: fn (Self, T, T) bool) ItemAndIndex {
fn bestDescendent(self: Self, first_child_index: usize, first_grandchild_index: usize, target_order: Order) ItemAndIndex {
const second_child_index = first_child_index + 1;
if (first_grandchild_index >= self.len) {
// No grandchildren, find the best child (second may not exist)
@ -313,24 +310,24 @@ pub fn PriorityDequeue(comptime T: type) type {
.index = first_child_index,
};
} else {
return self.bestItemAtIndices(first_child_index, second_child_index, compare);
return self.bestItemAtIndices(first_child_index, second_child_index, target_order);
}
}
const second_grandchild_index = first_grandchild_index + 1;
if (second_grandchild_index >= self.len) {
// One grandchild, so we know there is a second child. Compare first grandchild and second child
return self.bestItemAtIndices(first_grandchild_index, second_child_index, compare);
return self.bestItemAtIndices(first_grandchild_index, second_child_index, target_order);
}
const best_left_grandchild_index = self.bestItemAtIndices(first_grandchild_index, second_grandchild_index, compare).index;
const best_left_grandchild_index = self.bestItemAtIndices(first_grandchild_index, second_grandchild_index, target_order).index;
const third_grandchild_index = second_grandchild_index + 1;
if (third_grandchild_index >= self.len) {
// Two grandchildren, and we know the best. Compare this to second child.
return self.bestItemAtIndices(best_left_grandchild_index, second_child_index, compare);
return self.bestItemAtIndices(best_left_grandchild_index, second_child_index, target_order);
} else {
// Three grandchildren, compare the min of the first two with the third
return self.bestItemAtIndices(best_left_grandchild_index, third_grandchild_index, compare);
return self.bestItemAtIndices(best_left_grandchild_index, third_grandchild_index, target_order);
}
}
@ -348,12 +345,12 @@ pub fn PriorityDequeue(comptime T: type) type {
/// Dequeue takes ownership of the passed in slice. The slice must have been
/// allocated with `allocator`.
/// De-initialize with `deinit`.
pub fn fromOwnedSlice(allocator: *Allocator, lessThanFn: fn (T, T) bool, items: []T) Self {
pub fn fromOwnedSlice(allocator: *Allocator, compareFn: fn (T, T) Order, items: []T) Self {
var queue = Self{
.items = items,
.len = items.len,
.allocator = allocator,
.lessThanFn = lessThanFn,
.compareFn = compareFn,
};
if (queue.len <= 1) return queue;
@ -468,8 +465,8 @@ pub fn PriorityDequeue(comptime T: type) type {
};
}
fn lessThanComparison(a: u32, b: u32) bool {
return a < b;
fn lessThanComparison(a: u32, b: u32) Order {
return std.math.order(a, b);
}
const PDQ = PriorityDequeue(u32);
@ -493,6 +490,32 @@ test "std.PriorityDequeue: add and remove min" {
expectEqual(@as(u32, 54), queue.removeMin());
}
test "std.PriorityDequeue: add and remove min structs" {
const S = struct {
size: u32,
};
var queue = PriorityDequeue(S).init(testing.allocator, struct {
fn order(a: S, b: S) Order {
return std.math.order(a.size, b.size);
}
}.order);
defer queue.deinit();
try queue.add(.{ .size = 54 });
try queue.add(.{ .size = 12 });
try queue.add(.{ .size = 7 });
try queue.add(.{ .size = 23 });
try queue.add(.{ .size = 25 });
try queue.add(.{ .size = 13 });
expectEqual(@as(u32, 7), queue.removeMin().size);
expectEqual(@as(u32, 12), queue.removeMin().size);
expectEqual(@as(u32, 13), queue.removeMin().size);
expectEqual(@as(u32, 23), queue.removeMin().size);
expectEqual(@as(u32, 25), queue.removeMin().size);
expectEqual(@as(u32, 54), queue.removeMin().size);
}
test "std.PriorityDequeue: add and remove max" {
var queue = PDQ.init(testing.allocator, lessThanComparison);
defer queue.deinit();

41
lib/std/priority_queue.zig
View file

@ -7,6 +7,7 @@ const std = @import("std.zig");
const Allocator = std.mem.Allocator;
const assert = std.debug.assert;
const warn = std.debug.warn;
const Order = std.math.Order;
const testing = std.testing;
const expect = testing.expect;
const expectEqual = testing.expectEqual;
@ -20,15 +21,17 @@ pub fn PriorityQueue(comptime T: type) type {
items: []T,
len: usize,
allocator: *Allocator,
compareFn: fn (a: T, b: T) bool,
compareFn: fn (a: T, b: T) Order,
/// Initialize and return a priority queue. Provide
/// `compareFn` that returns `true` when its first argument
/// should get popped before its second argument. For example,
/// to make `pop` return the minimum value, provide
/// Initialize and return a priority queue. Provide `compareFn`
/// that returns `Order.lt` when its first argument should
/// get popped before its second argument, `Order.eq` if the
/// arguments are of equal priority, or `Order.gt` if the second
/// argument should be popped first. For example, to make `pop`
/// return the smallest number, provide
///
/// `fn lessThan(a: T, b: T) bool { return a < b; }`
pub fn init(allocator: *Allocator, compareFn: fn (a: T, b: T) bool) Self {
/// `fn lessThan(a: T, b: T) Order { return std.math.order(a, b); }`
pub fn init(allocator: *Allocator, compareFn: fn (a: T, b: T) Order) Self {
return Self{
.items = &[_]T{},
.len = 0,
@ -61,7 +64,7 @@ pub fn PriorityQueue(comptime T: type) type {
const child = self.items[child_index];
const parent = self.items[parent_index];
if (!self.compareFn(child, parent)) break;
if (self.compareFn(child, parent) != .lt) break;
self.items[parent_index] = child;
self.items[child_index] = parent;
@ -133,14 +136,14 @@ pub fn PriorityQueue(comptime T: type) type {
var smallest = self.items[index];
if (left) |e| {
if (self.compareFn(e, smallest)) {
if (self.compareFn(e, smallest) == .lt) {
smallest_index = left_index;
smallest = e;
}
}
if (right) |e| {
if (self.compareFn(e, smallest)) {
if (self.compareFn(e, smallest) == .lt) {
smallest_index = right_index;
smallest = e;
}
@ -159,7 +162,7 @@ pub fn PriorityQueue(comptime T: type) type {
/// PriorityQueue takes ownership of the passed in slice. The slice must have been
/// allocated with `allocator`.
/// Deinitialize with `deinit`.
pub fn fromOwnedSlice(allocator: *Allocator, compareFn: fn (a: T, b: T) bool, items: []T) Self {
pub fn fromOwnedSlice(allocator: *Allocator, compareFn: fn (a: T, b: T) Order, items: []T) Self {
var queue = Self{
.items = items,
.len = items.len,
@ -217,10 +220,10 @@ pub fn PriorityQueue(comptime T: type) type {
var update_index: usize = std.mem.indexOfScalar(T, self.items[0..self.len], elem) orelse return error.ElementNotFound;
const old_elem: T = self.items[update_index];
self.items[update_index] = new_elem;
if (self.compareFn(new_elem, old_elem)) {
siftUp(self, update_index);
} else {
siftDown(self, update_index);
switch (self.compareFn(new_elem, old_elem)) {
.lt => siftUp(self, update_index),
.gt => siftDown(self, update_index),
.eq => {}, // Nothing to do as the items have equal priority
}
}
@ -267,12 +270,12 @@ pub fn PriorityQueue(comptime T: type) type {
};
}
fn lessThan(a: u32, b: u32) bool {
return a < b;
fn lessThan(a: u32, b: u32) Order {
return std.math.order(a, b);
}
fn greaterThan(a: u32, b: u32) bool {
return a > b;
fn greaterThan(a: u32, b: u32) Order {
return lessThan(a, b).invert();
}
const PQ = PriorityQueue(u32);