65. Valid Number

Validate if a given string can be interpreted as a decimal number.

Some examples: "0" => true " 0.1 " => true "abc" => false "1 a" => false "2e10" => true " -90e3 " => true " 1e" => false "e3" => false " 6e-1" => true " 99e2.5 " => false "53.5e93" => true " --6 " => false "-+3" => false "95a54e53" => false

Note: It is intended for the problem statement to be ambiguous. It would be best if you gathered all requirements up front before implementing one. However, here is a list of characters that can be in a valid decimal number:

• Numbers 0-9
• Exponent - "e"
• Positive/negative sign - "+"/"-"
• Decimal point - "."

Of course, the context of these characters also matters in the input.

Example 1:

Input: s = "0"
Output: true

Example 2:

Input: s = "3"
Output: true

Constraints:

• 1 <= s.length <= 20
• s consists of only English letters, digits, space ' ', plus '+', minus '-', or dot '.'.

# @lc code=start
using LeetCode

# Automation
function is_number_65(s::String)::Bool
    # initialize state
    state = "start"
    # recognize input state
    function switch(c::Char)::Int
        isdigit(c) && return 1
        c == '.' && return 2
        c in "eE" && return 3
        c in "+-" && return 4
        return 5
    end
    state_shift = Dict{String,Vector{String}}(
        "start" => ["num", "dot_part", "error", "sign", "error"],
        "num" => ["num", "dot_num", "e_part", "error", "error"],
        "dot_num" => ["dot_num", "error", "e_part", "error", "error"],
        "e_num" => ["e_num", "error", "error", "error", "error"],
        "sign" => ["num", "dot_part", "error", "error", "error"],
        "dot_part" => ["dot_num", "error", "error", "error", "error"],
        "e_part" => ["e_num", "error", "error", "e_sign", "error"],
        "e_sign" => ["e_num", "error", "error", "error", "error"],
    )
    for c in s
        state = state_shift[state][switch(c)]
        state == "error" && return false
    end
    return state in ["num", "dot_num", "e_num"]
end
# @lc code=end

is_number_65 (generic function with 1 method)

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