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[priority_queue] Simplify sifting & fix edge case

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Validark 2023-06-23 13:18:56 -06:00 committed by Andrew Kelley
parent f1bd598768
commit 8b1976cab5
1 changed files with 21 additions and 41 deletions
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62
lib/std/priority_queue.zig
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@ -51,18 +51,16 @@ pub fn PriorityQueue(comptime T: type, comptime Context: type, comptime compareF
}
fn siftUp(self: *Self, start_index: usize) void {
const child = self.items[start_index];
var child_index = start_index;
while (child_index > 0) {
var parent_index = ((child_index - 1) >> 1);
const child = self.items[child_index];
const parent_index = ((child_index - 1) >> 1);
const parent = self.items[parent_index];
if (compareFn(self.context, child, parent) != .lt) break;
self.items[parent_index] = child;
self.items[child_index] = parent;
child_index = parent_index;
}
self.items[child_index] = child;
}
/// Add each element in `items` to the queue.
@ -128,61 +126,43 @@ pub fn PriorityQueue(comptime T: type, comptime Context: type, comptime compareF
return self.items.len;
}
fn siftDown(self: *Self, start_index: usize) void {
var index = start_index;
const half = self.len >> 1;
fn siftDown(self: *Self, target_index: usize) void {
const target_element = self.items[target_index];
var index = target_index;
while (true) {
var left_index = (index << 1) + 1;
var right_index = left_index + 1;
var left = if (left_index < self.len) self.items[left_index] else null;
var right = if (right_index < self.len) self.items[right_index] else null;
var lesser_child_i = (std.math.mul(usize, index, 2) catch break) | 1;
if (!(lesser_child_i < self.len)) break;
var smallest_index = index;
var smallest = self.items[index];
if (left) |e| {
if (compareFn(self.context, e, smallest) == .lt) {
smallest_index = left_index;
smallest = e;
}
const next_child_i = lesser_child_i + 1;
if (next_child_i < self.len and compareFn(self.context, self.items[next_child_i], self.items[lesser_child_i]) == .lt) {
lesser_child_i = next_child_i;
}
if (right) |e| {
if (compareFn(self.context, e, smallest) == .lt) {
smallest_index = right_index;
smallest = e;
}
}
if (compareFn(self.context, target_element, self.items[lesser_child_i]) == .lt) break;
if (smallest_index == index) return;
self.items[smallest_index] = self.items[index];
self.items[index] = smallest;
index = smallest_index;
if (index >= half) return;
self.items[index] = self.items[lesser_child_i];
index = lesser_child_i;
}
self.items[index] = target_element;
}
/// PriorityQueue takes ownership of the passed in slice. The slice must have been
/// allocated with `allocator`.
/// Deinitialize with `deinit`.
pub fn fromOwnedSlice(allocator: Allocator, items: []T, context: Context) Self {
var queue = Self{
var self = Self{
.items = items,
.len = items.len,
.allocator = allocator,
.context = context,
};
if (queue.len <= 1) return queue;
const half = (queue.len >> 1) - 1;
var i: usize = 0;
while (i <= half) : (i += 1) {
queue.siftDown(half - i);
var i = self.len >> 1;
while (i > 0) {
i -= 1;
self.siftDown(i);
}
return queue;
return self;
}
/// Ensure that the queue can fit at least `new_capacity` items.