submitted evaluate-reverse-polish-notation

[Runtime Error]
["4","-2","/","2","-3","-","-"]

isdigit detects "-2' incorrectly

Signed-off-by: Gui Chen <gui.g.chen@gmail.com>
resolved evaluate-reverse-polish-notation

[Accepted]

Signed-off-by: Gui Chen <gui.g.chen@gmail.com>
resolved palindrome-number

[Accepted]

Signed-off-by: Gui Chen <gui.g.chen@gmail.com>