Data commit

Task/Parsing-RPN-to-infix-conversion/Lua/parsing-rpn-to-infix-conversion.lua

@@ -0,0 +1,85 @@
+function tokenize(rpn)
+    local out = {}
+    local cnt = 0
+    for word in rpn:gmatch("%S+") do
+        table.insert(out, word)
+        cnt = cnt + 1
+    end
+    return {tokens = out, pos = 1, size = cnt}
+end
+
+function advance(lex)
+    if lex.pos <= lex.size then
+        lex.pos = lex.pos + 1
+        return true
+    else
+        return false
+    end
+end
+
+function current(lex)
+    return lex.tokens[lex.pos]
+end
+
+function isOperator(sym)
+    return sym == '+' or sym == '-'
+        or sym == '*' or sym == '/'
+        or sym == '^'
+end
+
+function buildTree(lex)
+    local stack = {}
+
+    while lex.pos <= lex.size do
+        local sym = current(lex)
+        advance(lex)
+
+        if isOperator(sym) then
+            local b = table.remove(stack)
+            local a = table.remove(stack)
+
+            local t = {op=sym, left=a, right=b}
+            table.insert(stack, t)
+        else
+            table.insert(stack, sym)
+        end
+    end
+
+    return table.remove(stack)
+end
+
+function infix(tree)
+    if type(tree) == "table" then
+        local a = {}
+        local b = {}
+
+        if type(tree.left) == "table" then
+            a = '(' .. infix(tree.left) .. ')'
+        else
+            a = tree.left
+        end
+
+        if type(tree.right) == "table" then
+            b = '(' .. infix(tree.right) .. ')'
+        else
+            b = tree.right
+        end
+
+        return a .. ' ' .. tree.op .. ' ' .. b
+    else
+        return tree
+    end
+end
+
+function convert(str)
+    local lex = tokenize(str)
+    local tree = buildTree(lex)
+    print(infix(tree))
+end
+
+function main()
+    convert("3 4 2 * 1 5 - 2 3 ^ ^ / +")
+    convert("1 2 + 3 4 + ^ 5 6 + ^")
+end
+
+main()