Add Zeckendorf in Euphoria (#5340)

Author: rzuckerm

archive/e/euphoria/zeckendorf.eu

@@ -0,0 +1,118 @@
+include std/io.e
+include std/types.e
+include std/text.e
+include std/get.e as stdget
+include std/sequence.e
+
+-- Indices for value() return value
+enum VALUE_ERROR_CODE, VALUE_VALUE, VALUE_NUM_CHARS_READ
+
+-- Indices for parse_int() return value
+enum PARSE_INT_VALID, PARSE_INT_VALUE
+
+function parse_int(sequence s)
+    -- Trim off whitespace and parse string
+    s = trim(s)
+    sequence result = stdget:value(s,, GET_LONG_ANSWER)
+
+    -- Error if any errors, value is not an integer, or any leftover characters
+    boolean valid = (
+        result[VALUE_ERROR_CODE] = GET_SUCCESS
+        and integer(result[VALUE_VALUE])
+        and result[VALUE_NUM_CHARS_READ] = length(s)
+    )
+
+    -- Get value if invalid
+    integer value = 0
+    if valid
+    then
+        value = result[VALUE_VALUE]
+    end if
+
+    return {valid, value}
+end function
+
+procedure usage()
+    puts(STDOUT, "Usage: please input a non-negative integer\n")
+    abort(0)
+end procedure
+
+procedure show_list_values(sequence values)
+    if length(values) > 0
+    then
+        sequence format = repeat_pattern("%d, ", length(values))
+        sequence s = sprintf(format[1..$-2], values)
+        printf(STDOUT, "%s\n", {s})
+    end if
+end procedure
+
+function get_fibonacci_values(integer value)
+    -- Initialize Fibonacci state:
+    -- fib(2) = 1
+    -- fib(3) = 2
+    sequence fibs = {}
+    integer a = 1
+    integer b = 2
+    integer t
+
+    -- Update Fibonacci state and store values
+    while a <= value
+    do
+        -- fib(n) = fib(n - 1) + fib(n - 2)
+        fibs &= a
+        t = a + b
+        a = b
+        b = t
+    end while
+
+    return fibs
+end function
+
+function get_zeckendorf_values(integer value)
+    sequence zecks = {}
+
+    -- Go through Fibonacci numbers in reverse order, stopping when
+    -- remaining value is zero
+    sequence fibs = get_fibonacci_values(value)
+    integer n = length(fibs)
+    while n > 0 and value > 0
+    do
+        -- If candidate Fibonacci number is greater than or equal to remaining value,
+        integer f = fibs[n]
+        if value >= f
+        then
+            -- Append Fibonacci number to result
+            zecks &= f
+
+            -- Reduce remaining value
+            value -= f
+
+            -- Skip previous value
+            n -= 2
+        -- Else, go to previous value
+        else
+            n -= 1
+        end if
+    end while
+
+    return zecks
+end function
+
+-- Check 1st command-line argument
+sequence argv = command_line()
+if length(argv) < 4 or length(argv[4]) = 0
+then
+    usage()
+end if
+
+-- Parse 1st command-line argument
+sequence result = parse_int(argv[4])
+integer value = result[PARSE_INT_VALUE]
+if not result[PARSE_INT_VALID] or value < 0
+then
+    usage()
+end if
+
+--Get Zeckendorf values
+sequence values = get_zeckendorf_values(value)
+show_list_values(values)