From a22d229c0179f2096d6a9bc929401a25d64384f9 Mon Sep 17 00:00:00 2001
From: Dany Thach <d.thach4@gmail.com>
Date: Sat, 15 Feb 2025 19:40:47 +0100
Subject: [PATCH] Fix: heap sift-down to the right happened even when it
 shouldn't have

---
 lib/data_structures/search_heap.dart | 53 +++++++++++++++++++---------
 1 file changed, 36 insertions(+), 17 deletions(-)

diff --git a/lib/data_structures/search_heap.dart b/lib/data_structures/search_heap.dart
index b44d87c..f0b4d63 100644
--- a/lib/data_structures/search_heap.dart
+++ b/lib/data_structures/search_heap.dart
@@ -3,14 +3,14 @@ class SearchHeap<K, T> {
   final K Function(T) getKey;
   final int Function(T) getPriority;
   List<(T, K, int)> _items;
-  Map<K, int> _positionByKey;
+  Map<K, int> _indexByKey;
 
   SearchHeap({
     required this.getKey,
     required this.getPriority,
   }):
     _items = [],
-    _positionByKey = {};
+    _indexByKey = {};
 
   factory SearchHeap.fromItems(
     List<T> items,
@@ -43,11 +43,11 @@ class SearchHeap<K, T> {
     _items.add(heapItem);
     while (i > 0 && _items[(i-1) >> 1].$3 > thisKey) {
       _items[i] = _items[(i-1) >> 1];
-      _positionByKey[_items[i].$2] = i;
+      _indexByKey[_items[i].$2] = i;
       i = (i-1) >> 1;
     }
     _items[i] = heapItem;
-    _positionByKey[heapItem.$2] = i;
+    _indexByKey[heapItem.$2] = i;
   }
 
   T removeFirst() {
@@ -55,7 +55,7 @@ class SearchHeap<K, T> {
       throw StateError("No element");
     }
     final T firstItem = _items[0].$1;
-    _positionByKey.remove(_items[0].$2);
+    _indexByKey.remove(_items[0].$2);
     if (_items.length < 2) {
       _items.length--;
       return firstItem;
@@ -71,34 +71,34 @@ class SearchHeap<K, T> {
       if (leftIndex < _items.length && itemToMove.$3 > _items[leftIndex].$3) {
         if (rightIndex < _items.length && _items[leftIndex].$3 > _items[rightIndex].$3) {
           _items[i] = _items[rightIndex];
-          _positionByKey[_items[i].$2] = i;
+          _indexByKey[_items[i].$2] = i;
           i = rightIndex;
         } else {
           _items[i] = _items[leftIndex];
-          _positionByKey[_items[i].$2] = i;
+          _indexByKey[_items[i].$2] = i;
           i = leftIndex;
         }
-      } else if (rightIndex < _items.length && _items[leftIndex].$3 > _items[rightIndex].$3) {
+      } else if (rightIndex < _items.length && itemToMove.$3 > _items[rightIndex].$3) {
         _items[i] = _items[rightIndex];
-        _positionByKey[_items[i].$2] = i;
+        _indexByKey[_items[i].$2] = i;
         i = rightIndex;
       } else {
         stop = true;
       }
     }
     _items[i] = itemToMove;
-    _positionByKey[itemToMove.$2] = i;
+    _indexByKey[itemToMove.$2] = i;
     return firstItem;
   }
 
   void updateElement(K key) {
-    int i = _positionByKey[key]!;
+    int i = _indexByKey[key]!;
     final (T, K, int) item = (_items[i].$1, _items[i].$2, getPriority(_items[i].$1));
     bool dontBubbleDown = false;
     while (i > 0 && _items[(i-1) >> 1].$3 > item.$3) {
       dontBubbleDown = true;
       _items[i] = _items[(i-1) >> 1];
-      _positionByKey[_items[i].$2] = i;
+      _indexByKey[_items[i].$2] = i;
       i = (i-1) >> 1;
     }
     int leftIndex, rightIndex;
@@ -108,28 +108,47 @@ class SearchHeap<K, T> {
       if (leftIndex < _items.length && item.$3 > _items[leftIndex].$3) {
         if (rightIndex < _items.length && _items[leftIndex].$3 > _items[rightIndex].$3) {
           _items[i] = _items[rightIndex];
-          _positionByKey[_items[i].$2] = i;
+          _indexByKey[_items[i].$2] = i;
           i = rightIndex;
         } else {
           _items[i] = _items[leftIndex];
-          _positionByKey[_items[i].$2] = i;
+          _indexByKey[_items[i].$2] = i;
           i = leftIndex;
         }
-      } else if (rightIndex < _items.length && _items[leftIndex].$3 > _items[rightIndex].$3) {
+      } else if (rightIndex < _items.length && item.$3 > _items[rightIndex].$3) {
         _items[i] = _items[rightIndex];
-        _positionByKey[_items[i].$2] = i;
+        _indexByKey[_items[i].$2] = i;
         i = rightIndex;
       } else {
         dontBubbleDown = true;
       }
     }
     _items[i] = item;
-    _positionByKey[item.$2] = i;
+    _indexByKey[item.$2] = i;
   }
 
   @override
   String toString() => _items.map(((T, K, int) item) => item.$1).toString();
 
   List<T> get debugItems => _items.map(((T, K, int) item) => item.$1).toList();
+  Map<K, int> get debugPositionByKey => _indexByKey;
+
+  bool get debugHeapValidity {
+    for (int i = 1; i < _items.length; i++) {
+      if (_items[i].$3 < _items[(i-1) >> 1].$3) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  bool get debugDictionaryValidity {
+    for (final MapEntry<K, int>(key: K key, value: int index) in _indexByKey.entries) {
+      if (_items[index].$2 != key) {
+        return false;
+      }
+    }
+    return true;
+  }
 
 }
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