From ce7a4a930f31b6cb0c3c35d5513939369802e7cf Mon Sep 17 00:00:00 2001
From: Oleksii Trekhleb <trehleb@gmail.com>
Date: Thu, 3 May 2018 06:47:09 +0300
Subject: [PATCH] Add Dijkstra.

---
 src/algorithms/graph/dijkstra/dijkstra.js     |  9 ++++-
 .../priority-queue/PriorityQueue.js           | 38 +++++++++++++++----
 .../__test__/PriorityQueue.test.js            | 13 +++++++
 3 files changed, 51 insertions(+), 9 deletions(-)

diff --git a/src/algorithms/graph/dijkstra/dijkstra.js b/src/algorithms/graph/dijkstra/dijkstra.js
index 5e192feb..439efce3 100644
--- a/src/algorithms/graph/dijkstra/dijkstra.js
+++ b/src/algorithms/graph/dijkstra/dijkstra.js
@@ -33,10 +33,17 @@ export default function dijkstra(graph, startVertex) {
 
         if (distanceToNeighborFromCurrent < existingDistanceToNeighbor) {
           distances[neighbor.getKey()] = distanceToNeighborFromCurrent;
+
+          // Change priority.
+          if (queue.hasValue(neighbor)) {
+            queue.changePriority(neighbor, distances[neighbor.getKey()]);
+          }
         }
 
         // Add neighbor to the queue for further visiting.
-        queue.add(neighbor, distances[neighbor.getKey()]);
+        if (!queue.hasValue(neighbor)) {
+          queue.add(neighbor, distances[neighbor.getKey()]);
+        }
       }
     });
 
diff --git a/src/data-structures/priority-queue/PriorityQueue.js b/src/data-structures/priority-queue/PriorityQueue.js
index 32538a61..2bf27bb3 100644
--- a/src/data-structures/priority-queue/PriorityQueue.js
+++ b/src/data-structures/priority-queue/PriorityQueue.js
@@ -40,19 +40,28 @@ export default class PriorityQueue extends MinHeap {
    * @return {PriorityQueue}
    */
   changePriority(item, priority) {
-    const customFindingComparator = new Comparator((a, b) => {
-      if (a === b) {
-        return 0;
-      }
-      return a < b ? -1 : 1;
-    });
-
-    this.remove(item, customFindingComparator);
+    this.remove(item, new Comparator(this.compareValue));
     this.add(item, priority);
 
     return this;
   }
 
+  /**
+   * @param {*} item
+   * @return {Number[]}
+   */
+  findByValue(item) {
+    return this.find(item, new Comparator(this.compareValue));
+  }
+
+  /**
+   * @param {*} item
+   * @return {boolean}
+   */
+  hasValue(item) {
+    return this.findByValue(item).length > 0;
+  }
+
   /**
    * @param {*} a
    * @param {*} b
@@ -65,4 +74,17 @@ export default class PriorityQueue extends MinHeap {
 
     return this.priorities[a] < this.priorities[b] ? -1 : 1;
   }
+
+  /**
+   * @param {*} a
+   * @param {*} b
+   * @return {number}
+   */
+  compareValue(a, b) {
+    if (a === b) {
+      return 0;
+    }
+
+    return a < b ? -1 : 1;
+  }
 }
diff --git a/src/data-structures/priority-queue/__test__/PriorityQueue.test.js b/src/data-structures/priority-queue/__test__/PriorityQueue.test.js
index 5d3a20fa..e5f490cd 100644
--- a/src/data-structures/priority-queue/__test__/PriorityQueue.test.js
+++ b/src/data-structures/priority-queue/__test__/PriorityQueue.test.js
@@ -87,4 +87,17 @@ describe('PriorityQueue', () => {
     expect(priorityQueue.poll()).toBe(15);
     expect(priorityQueue.poll()).toBe(10);
   });
+
+  it('should be possible to search in priority queue by value', () => {
+    const priorityQueue = new PriorityQueue();
+
+    priorityQueue.add(10, 1);
+    priorityQueue.add(5, 2);
+    priorityQueue.add(100, 0);
+    priorityQueue.add(200, 0);
+    priorityQueue.add(15, 15);
+
+    expect(priorityQueue.hasValue(70)).toBeFalsy();
+    expect(priorityQueue.hasValue(15)).toBeTruthy();
+  });
 });