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src/util.jl

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+module util
+
+export UCTselect
+
+using ..type
+
+# ---------------------------------------------- 100 --------------------------------------------- #
+
+""" Select a node based on UCT score
+
+# Arguments
+  - `node::MCTSNode`
+    mcts node
+  - `w::T`
+    exploration weight. Value is usually between 1 to 2. 
+    Value 1.0 makes MCTS balance between exploration and exploitation like 50%-50%.
+    Value 2.0 makes MCTS aggressively search the tree.
+# Return
+  - `selectedNode::MCTSNode`
+
+# Example
+```jldoctest
+julia> 
+```
+
+# Signature
+"""
+function UCTselect(node::MCTSNode, w::T)::MCTSNode where {T<:AbstractFloat}
+  maxUCT = -Inf
+  selectedNode = nothing
+
+  for (childState, childNode) in node.children
+    UCTvalue =
+    if childNode.visits != 0  
+      weightedterm = w * sqrt(log(node.visits) / childNode.visits) # explore term
+      childNode.statevalue + weightedterm
+    else  # node.visits == 0 makes sqrt() in explore term error
+      childNode.progressvalue  # exploit term
+    end
+                
+    if UCTvalue > maxUCT
+      maxUCT = UCTvalue
+        selectedNode = childNode
+    end
+  end
+
+  return selectedNode
+end
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+end # module util