Coderforces#137 (Div. 2 - A)
Rubyの勉強がてらにCodeforcesの問題を解いてみた。
http://www.codeforces.com/contest/222/problem/A
def solve(k, a) t = a[k - 1] # kより後ろの配列 other = a[k - 1 .. -1] other.each do |i| if i != t return -1 end end c = 0 (k - 1).downto(0) do |idx| if a[idx - 1] != t return idx end end return c end n, k = gets.chomp.split(" ").map{|e| e.to_i} a = gets.chomp.split(" ").map{|e| e.to_i} puts solve(k, a)