added problem 1557

Author: SHA65536

problems/problem1557/min_verts.go

@@ -0,0 +1,26 @@
+package problem1557
+
+/*
+Given a directed acyclic graph, with n vertices numbered from 0 to n-1,
+and an array edges where edges[i] = [fromi, toi] represents a directed edge from node fromi to node toi.
+Find the smallest set of vertices from which all nodes in the graph are reachable.
+It's guaranteed that a unique solution exists.
+Notice that you can return the vertices in any order.
+*/
+
+func findSmallestSetOfVertices(n int, edges [][]int) []int {
+	var verts = make([]bool, n)
+	var res = make([]int, 0, n)
+	// Loop over edges to see which ones don't
+	// have incoming arrows
+	for _, e := range edges {
+		verts[e[1]] = true
+	}
+	// Add verts with no incoming arrows
+	for i := range verts {
+		if !verts[i] {
+			res = append(res, i)
+		}
+	}
+	return res
+}

problems/problem1557/min_verts_test.go

@@ -0,0 +1,37 @@
+package problem1557
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+type Result struct {
+	N        int
+	Input    [][]int
+	Expected []int
+}
+
+var Results = []Result{
+	{6, [][]int{{0, 1}, {0, 2}, {2, 5}, {3, 4}, {4, 2}}, []int{0, 3}},
+	{5, [][]int{{0, 1}, {2, 1}, {3, 1}, {1, 4}, {2, 4}}, []int{0, 2, 3}},
+}
+
+func TestMinVertsToReachAll(t *testing.T) {
+	assert := assert.New(t)
+
+	for _, res := range Results {
+		want := res.Expected
+		got := findSmallestSetOfVertices(res.N, res.Input)
+		assert.Equal(want, got, fmt.Sprintf("%+v", res))
+	}
+}
+
+func BenchmarkMinVertsToReachAll(b *testing.B) {
+	for i := 0; i < b.N; i++ {
+		for _, res := range Results {
+			findSmallestSetOfVertices(res.N, res.Input)
+		}
+	}
+}

readme.md

@@ -402,6 +402,7 @@ Each problem is in it's own directory, with test files. There are helper package
 | 1523 | [Count Odd Numbers in an Interval Range](https://leetcode.com/problems/count-odd-numbers-in-an-interval-range) | [My Solution](./problems/problem1523) | ✅ |
 | 1539 | [Kth Missing Positive Number](https://leetcode.com/problems/kth-missing-positive-number) | [My Solution](./problems/problem1539) | ✅ |
 | 1544 | [Make The String Great](https://leetcode.com/problems/make-the-string-great) | [My Solution](./problems/problem1544) | ✅ |
+| 1557 | [Minimum Number of Vertices to Reach All Nodes](https://leetcode.com/problems/minimum-number-of-vertices-to-reach-all-nodes) | [My Solution](./problems/problem1557) | ✅ |
 | 1572 | [Matrix Diagonal Sum](https://leetcode.com/problems/matrix-diagonal-sum) | [My Solution](./problems/problem1572) | ✅ |
 | 1578 | [Minimum Time to Make Rope Colorful](https://leetcode.com/problems/minimum-time-to-make-rope-colorful) | [My Solution](./problems/problem1578) | ✅ |
 | 1579 | [Remove Max Number of Edges to Keep Graph Fully Traversable](https://leetcode.com/problems/remove-max-number-of-edges-to-keep-graph-fully-traversable) | [My Solution](./problems/problem1579) | ✅ |