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// Copyright ©2014 The gonum Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
package graph
// Node is a graph node. It returns a graph-unique integer ID.
type Node interface {
ID() int
// Edge is a graph edge. In directed graphs, the direction of the
// edge is given from -> to, otherwise the edge is semantically
// unordered.
type Edge interface {
From() Node
To() Node
Weight() float64
// Graph is a generalized graph.
type Graph interface {
// Has returns whether the node exists within the graph.
Has(Node) bool
// Nodes returns all the nodes in the graph.
Nodes() []Node
// From returns all nodes that can be reached directly
// from the given node.
From(Node) []Node
// HasEdgeBeteen returns whether an edge exists between
// nodes x and y without considering direction.
HasEdgeBetween(x, y Node) bool
// Edge returns the edge from u to v if such an edge
// exists and nil otherwise. The node v must be directly
// reachable from u as defined by the From method.
Edge(u, v Node) Edge
// Undirected is an undirected graph.
type Undirected interface {
// EdgeBetween returns the edge between nodes x and y.
EdgeBetween(x, y Node) Edge
// Directed is a directed graph.
type Directed interface {
// HasEdgeFromTo returns whether an edge exists
// in the graph from u to v.
HasEdgeFromTo(u, v Node) bool
// To returns all nodes that can reach directly
// to the given node.
To(Node) []Node
// Weighter defines graphs that can report edge weights.
type Weighter interface {
// Weight returns the weight for the edge between
// x and y if Edge(x, y) returns a non-nil Edge.
// If x and y are the same node or there is no
// joining edge between the two nodes the weight
// value returned is implementation dependent.
// Weight returns true if an edge exists between
// x and y or if x and y have the same ID, false
// otherwise.
Weight(x, y Node) (w float64, ok bool)
// NodeAdder is an interface for adding arbitrary nodes to a graph.
type NodeAdder interface {
// NewNodeID returns a new unique arbitrary ID.
NewNodeID() int
// Adds a node to the graph. AddNode panics if
// the added node ID matches an existing node ID.
// NodeRemover is an interface for removing nodes from a graph.
type NodeRemover interface {
// RemoveNode removes a node from the graph, as
// well as any edges attached to it. If the node
// is not in the graph it is a no-op.
// EdgeSetter is an interface for adding edges to a graph.
type EdgeSetter interface {
// SetEdge adds an edge from one node to another.
// If the graph supports node addition the nodes
// will be added if they do not exist, otherwise
// SetEdge will panic.
// If the IDs returned by e.From and e.To are
// equal, SetEdge will panic.
SetEdge(e Edge)
// EdgeRemover is an interface for removing nodes from a graph.
type EdgeRemover interface {
// RemoveEdge removes the given edge, leaving the
// terminal nodes. If the edge does not exist it
// is a no-op.
// Builder is a graph that can have nodes and edges added.
type Builder interface {
// UndirectedBuilder is an undirected graph builder.
type UndirectedBuilder interface {
// DirectedBuilder is a directed graph builder.
type DirectedBuilder interface {
// Copy copies nodes and edges as undirected edges from the source to the destination
// without first clearing the destination. Copy will panic if a node ID in the source
// graph matches a node ID in the destination.
// If the source is undirected and the destination is directed both directions will
// be present in the destination after the copy is complete.
// If the source is a directed graph, the destination is undirected, and a fundamental
// cycle exists with two nodes where the edge weights differ, the resulting destination
// graph's edge weight between those nodes is undefined. If there is a defined function
// to resolve such conflicts, an Undirect may be used to do this.
func Copy(dst Builder, src Graph) {
nodes := src.Nodes()
for _, n := range nodes {
for _, u := range nodes {
for _, v := range src.From(u) {
dst.SetEdge(src.Edge(u, v))
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