Merge pull request #380 from 0xff-dev/1971

Add solution and test-cases for problem 1971

Author: Cori1109

leetcode/1901-2000/1971.Find-if-Path-Exists-in-Graph/README.md

@@ -1,28 +1,33 @@
 # [1971.Find if Path Exists in Graph][title]
 
-> [!WARNING|style:flat]
-> This question is temporarily unanswered if you have good ideas. Welcome to [Create Pull Request PR](https://github.com/kylesliu/awesome-golang-algorithm)
-
 ## Description
+There is a **bi-directional** graph with `n` vertices, where each vertex is labeled from `0` to `n - 1` (**inclusive**). The edges in the graph are represented as a 2D integer array `edges`, where each `edges[i] = [ui, vi]` denotes a bi-directional edge between vertex u<sub>i</sub> and vertex v<sub>i</sub>. Every vertex pair is connected by **at most one** edge, and no vertex has an edge to itself.
+
+You want to determine if there is a **valid path** that exists from vertex `source` to vertex `destination`.
+
+Given `edges` and the integers `n`, `source`, and `destination`, return `true` if there is a **valid path** from `source` to `destination`, or `false` otherwise.
 
-**Example 1:**
+**Example 1:**  
+
+![example1](./validpath-ex1.png)
 
 ```
-Input: a = "11", b = "1"
-Output: "100"
+Input: n = 3, edges = [[0,1],[1,2],[2,0]], source = 0, destination = 2
+Output: true
+Explanation: There are two paths from vertex 0 to vertex 2:
+- 0 → 1 → 2
+- 0 → 2
 ```
 
-## 题意
-> ...
+**Example 2:**  
 
-## 题解
+![example2](./validpath-ex2.png)
 
-### 思路1
-> ...
-Find if Path Exists in Graph
-```go
 ```
-
+Input: n = 6, edges = [[0,1],[0,2],[3,5],[5,4],[4,3]], source = 0, destination = 5
+Output: false
+Explanation: There is no path from vertex 0 to vertex 5.
+```
 
 ## 结语
 

leetcode/1901-2000/1971.Find-if-Path-Exists-in-Graph/Solution.go

@@ -1,5 +1,81 @@
 package Solution
 
-func Solution(x bool) bool {
-	return x
+func Solution(n int, edges [][]int, source int, destination int) bool {
+	graph := make(map[int]map[int]struct{})
+	for _, e := range edges {
+		if _, ok := graph[e[0]]; !ok {
+			graph[e[0]] = make(map[int]struct{})
+		}
+		if _, ok := graph[e[1]]; !ok {
+			graph[e[1]] = make(map[int]struct{})
+		}
+
+		graph[e[0]][e[1]] = struct{}{}
+		graph[e[1]][e[0]] = struct{}{}
+	}
+
+	visited := map[int]struct{}{}
+	visited[source] = struct{}{}
+	found := false
+	var dfs func(int, *bool)
+	dfs = func(source int, found *bool) {
+		if *found {
+			return
+		}
+		for rel := range graph[source] {
+			if _, ok := visited[rel]; ok {
+				continue
+			}
+			if rel == destination {
+				*found = true
+				return
+			}
+			visited[rel] = struct{}{}
+			dfs(rel, found)
+			delete(visited, rel)
+		}
+	}
+	dfs(source, &found)
+	return found
+}
+
+func Solution1(n int, edges [][]int, source int, destination int) bool {
+	if source == destination {
+		return true
+	}
+	graph := make(map[int]map[int]struct{})
+	for _, e := range edges {
+		if _, ok := graph[e[0]]; !ok {
+			graph[e[0]] = make(map[int]struct{})
+		}
+		if _, ok := graph[e[1]]; !ok {
+			graph[e[1]] = make(map[int]struct{})
+		}
+
+		graph[e[0]][e[1]] = struct{}{}
+		graph[e[1]][e[0]] = struct{}{}
+	}
+
+	queue := []int{source}
+
+	visited := map[int]struct{}{}
+	visited[source] = struct{}{}
+
+	for len(queue) > 0 {
+		nq := make([]int, 0)
+		for _, item := range queue {
+			for rel := range graph[item] {
+				if rel == destination {
+					return true
+				}
+
+				if _, ok := visited[rel]; !ok {
+					visited[rel] = struct{}{}
+					nq = append(nq, rel)
+				}
+			}
+		}
+		queue = nq
+	}
+	return false
 }

leetcode/1901-2000/1971.Find-if-Path-Exists-in-Graph/Solution_test.go

@@ -10,21 +10,37 @@ func TestSolution(t *testing.T) {
 	//	测试用例
 	cases := []struct {
 		name   string
-		inputs bool
+		n int
+		edges [][]int
+		source, destination int
 		expect bool
 	}{
-		{"TestCase", true, true},
-		{"TestCase", true, true},
-		{"TestCase", false, false},
+		{"TestCase1", 3, [][]int{
+		{0, 1},
+		{1, 2},
+		{2, 0},
+	}, 0, 2, true},
+		{"TestCase2", 6, [][]int{
+		{0, 1},
+		{0, 2},
+		{3, 5},
+		{5, 4},
+		{4, 3},
+	}, 0, 5, false},
 	}
 
 	//	开始测试
 	for i, c := range cases {
 		t.Run(c.name+" "+strconv.Itoa(i), func(t *testing.T) {
-			got := Solution(c.inputs)
+			got := Solution(c.n, c.edges, c.source, c.destination)
 			if !reflect.DeepEqual(got, c.expect) {
-				t.Fatalf("expected: %v, but got: %v, with inputs: %v",
-					c.expect, got, c.inputs)
+				t.Fatalf("expected: %v, but got: %v, with inputs: %v %v %v %v",
+					c.expect, got, c.n, c.edges, c.source, c.destination)
+			}
+			got = Solution1(c.n, c.edges, c.source, c.destination)
+			if !reflect.DeepEqual(got, c.expect) {
+				t.Fatalf("expected: %v, but got: %v, with inputs: %v %v %v %v",
+					c.expect, got, c.n, c.edges, c.source, c.destination)
 			}
 		})
 	}