add 1971

Author: fishercoder1534

README.md

@@ -35,6 +35,7 @@ _If you like this project, please leave me a star._ ★
 |1980|[Find Unique Binary String](https://leetcode.com/problems/find-unique-binary-string/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1980.java) ||Medium||
 |1979|[Find Greatest Common Divisor of Array](https://leetcode.com/problems/find-greatest-common-divisor-of-array/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1979.java) ||Easy||
 |1974|[Minimum Time to Type Word Using Special Typewriter](https://leetcode.com/problems/minimum-time-to-type-word-using-special-typewriter/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1974.java) ||Easy||
+|1971|[Find if Path Exists in Graph](https://leetcode.com/problems/find-if-path-exists-in-graph/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1971.java) ||Easy|BFS, DFS, Graph|
 |1968|[Array With Elements Not Equal to Average of Neighbors](https://leetcode.com/problems/array-with-elements-not-equal-to-average-of-neighbors/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1968.java) ||Medium||
 |1967|[Number of Strings That Appear as Substrings in Word](https://leetcode.com/problems/number-of-strings-that-appear-as-substrings-in-word/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1967.java) ||Easy||
 |1961|[Check If String Is a Prefix of Array](https://leetcode.com/problems/check-if-string-is-a-prefix-of-array/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_1961.java) ||Easy||

src/main/java/com/fishercoder/solutions/_1971.java

@@ -0,0 +1,49 @@
+package com.fishercoder.solutions;
+
+import java.util.HashMap;
+import java.util.HashSet;
+import java.util.LinkedList;
+import java.util.Map;
+import java.util.Queue;
+import java.util.Set;
+
+public class _1971 {
+    public static class Solution1 {
+        public boolean validPath(int n, int[][] edges, int start, int end) {
+            if (start == end) {
+                return true;
+            }
+            Map<Integer, Set<Integer>> neighborsMap = new HashMap<>();
+            for (int[] edge : edges) {
+                int u = edge[0];
+                int v = edge[1];
+                Set<Integer> neighbors1 = neighborsMap.getOrDefault(u, new HashSet<>());
+                neighbors1.add(v);
+                neighborsMap.put(u, neighbors1);
+
+                Set<Integer> neighbors2 = neighborsMap.getOrDefault(v, new HashSet<>());
+                neighbors2.add(u);
+                neighborsMap.put(v, neighbors2);
+            }
+            Queue<Integer> queue = new LinkedList<>();
+            Set<Integer> visitedVertices = new HashSet<>();
+            queue.offer(start);
+            while (!queue.isEmpty()) {
+                int size = queue.size();
+                for (int i = 0; i < size; i++) {
+                    Integer curr = queue.poll();
+                    for (int neighbor : neighborsMap.getOrDefault(curr, new HashSet<>())) {
+                        if (neighbor == end) {
+                            return true;
+                        }
+                        if (visitedVertices.add(neighbor)) {
+                            queue.offer(neighbor);
+                        }
+                    }
+                }
+            }
+            return false;
+        }
+
+    }
+}

src/test/java/com/fishercoder/_1971Test.java

@@ -0,0 +1,47 @@
+package com.fishercoder;
+
+import com.fishercoder.common.utils.CommonUtils;
+import com.fishercoder.solutions._1971;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class _1971Test {
+    private static _1971.Solution1 solution1;
+
+    @BeforeClass
+    public static void setup() {
+        solution1 = new _1971.Solution1();
+    }
+
+    @Test
+    public void test1() {
+        int[][] edges = CommonUtils.convertLeetCodeIrregularLengths2DArrayInputIntoJavaArray("[0,1],[1,2],[2,0]");
+        assertEquals(true, solution1.validPath(3, edges, 0, 2));
+    }
+
+    @Test
+    public void test2() {
+        int[][] edges = CommonUtils.convertLeetCodeIrregularLengths2DArrayInputIntoJavaArray("[0,1],[0,2],[3,5],[5,4],[4,3]");
+        assertEquals(false, solution1.validPath(6, edges, 0, 5));
+    }
+
+    @Test
+    public void test3() {
+        int[][] edges = CommonUtils.convertLeetCodeIrregularLengths2DArrayInputIntoJavaArray("[4,3],[1,4],[4,8],[1,7],[6,4],[4,2],[7,4],[4,0],[0,9],[5,4]");
+        assertEquals(true, solution1.validPath(10, edges, 5, 9));
+    }
+
+    @Test
+    public void test4() {
+        int[][] edges = CommonUtils.convertLeetCodeIrregularLengths2DArrayInputIntoJavaArray("[0,7],[0,8],[6,1],[2,0],[0,4],[5,8],[4,7],[1,3],[3,5],[6,5]");
+        assertEquals(true, solution1.validPath(10, edges, 7, 5));
+    }
+
+    @Test
+    public void test5() {
+        assertEquals(true, solution1.validPath(1, new int[][]{}, 0, 0));
+    }
+
+}