added problem 1361

Author: SHA65536

problems/problem1361/validate_tree.go

@@ -0,0 +1,81 @@
+package problem1361
+
+/*
+You have n binary tree nodes numbered from 0 to n - 1 where node i has two children leftChild[i] and rightChild[i],
+return true if and only if all the given nodes form exactly one valid binary tree.
+If node i has no left child then leftChild[i] will equal -1, similarly for the right child.
+Note that the nodes have no values and that we only use the node numbers in this problem.
+*/
+
+func validateBinaryTreeNodes(n int, leftChild []int, rightChild []int) bool {
+	// uf[i] represents the group that is the parent of group i
+	var uf = make([]int, n)
+	// indegree[i] represents how many nodes lead to node i
+	var indegree = make([]int, n)
+
+	// Initialize the disjoint set (union find) group
+	for i := range uf {
+		uf[i] = i
+	}
+
+	// Loop over the nodes and build the graph
+	for i := 0; i < n; i++ {
+		// If the is a child node
+		if leftChild[i] != -1 {
+			// Increment the node's indegree
+			indegree[leftChild[i]]++
+			// Update the parent graph
+			union(uf, leftChild[i], i)
+		}
+
+		// Same for right child
+		if rightChild[i] != -1 {
+			indegree[rightChild[i]]++
+			union(uf, rightChild[i], i)
+		}
+	}
+
+	// There should be only 1 root (a node with no indegree)
+	var foundRoot = false
+	for i := range indegree {
+		if indegree[i] > 1 {
+			return false
+		}
+		if indegree[i] == 0 {
+			if foundRoot {
+				return false
+			}
+			foundRoot = true
+		}
+	}
+
+	// Find how many different groups there are
+	var uniqGroups = map[int]bool{}
+	for i := range uf {
+		uniqGroups[find(uf, i)] = true
+	}
+
+	// There should be only one group and one root
+	return len(uniqGroups) == 1 && foundRoot
+}
+
+func find(uf []int, x int) int {
+	if uf[x] == x {
+		// If x is the parent of itself, it is the root of the group
+		return uf[x]
+	} else {
+		// If x is not the parent of itself, we call this function again
+		// to find the real parent, and update the map
+		uf[x] = find(uf, uf[x])
+		return uf[x]
+	}
+}
+
+func union(uf []int, x, y int) {
+	var rootx, rooty int
+	// Finding the roots of x and y
+	rootx = find(uf, x)
+	rooty = find(uf, y)
+	// Setting the root of rootx be rooty effectivly merging the groups
+	uf[rootx] = rooty
+}

problems/problem1361/validate_tree_test.go

@@ -0,0 +1,39 @@
+package problem1361
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+type TestCase struct {
+	N           int
+	Left, Right []int
+	Expected    bool
+}
+
+var TestCases = []TestCase{
+	//{4, []int{1, -1, 3, -1}, []int{2, -1, -1, -1}, true},
+	//{4, []int{1, -1, 3, -1}, []int{2, 3, -1, -1}, false},
+	//{2, []int{1, 0}, []int{-1, -1}, false},
+	{4, []int{1, 2, 0, -1}, []int{-1, -1, -1, -1}, false},
+}
+
+func TestValidateBinaryTree(t *testing.T) {
+	assert := assert.New(t)
+
+	for _, tc := range TestCases {
+		want := tc.Expected
+		got := validateBinaryTreeNodes(tc.N, tc.Left, tc.Right)
+		assert.Equal(want, got, fmt.Sprintf("%+v", tc))
+	}
+}
+
+func BenchmarkValidateBinaryTree(b *testing.B) {
+	for _, tc := range TestCases {
+		for i := 0; i < b.N; i++ {
+			validateBinaryTreeNodes(tc.N, tc.Left, tc.Right)
+		}
+	}
+}

readme.md

@@ -440,6 +440,7 @@ Each problem is in it's own directory, with test files. There are helper package
 | 1351 | [Count Negative Numbers in a Sorted Matrix](https://leetcode.com/problems/count-negative-numbers-in-a-sorted-matrix) | [My Solution](./problems/problem1351) | ✅ | 
 | 1354 | [Construct Target Array With Multiple Sums](https://leetcode.com/problems/construct-target-array-with-multiple-sums) | [My Solution](./problems/problem1354) | ✅ |
 | 1357 | [Apply Discount Every n Orders](https://leetcode.com/problems/apply-discount-every-n-orders) | [My Solution](./problems/problem1357) | ✅ |
+| 1361 | [Validate Binary Tree Nodes](https://leetcode.com/problems/validate-binary-tree-nodes) | [My Solution](./problems/problem1361) | ✅ |
 | 1372 | [Longest ZigZag Path in a Binary Tree](https://leetcode.com/problems/longest-zigzag-path-in-a-binary-tree) | [My Solution](./problems/problem1372) | ✅ |
 | 1376 | [Time Needed to Inform All Employees](https://leetcode.com/problems/time-needed-to-inform-all-employees) | [My Solution](./problems/problem1376) | ✅ |
 | 1379 | [Find a Binary Tree Node in a Clone of That Tree*](https://leetcode.com/problems/find-a-corresponding-node-of-a-binary-tree-in-a-clone-of-that-tree) | [My Solution](./problems/problem1379) | ✅ |