#/***********************************************************
#    select.rb -- 選択
#***********************************************************/

def select(a,  n,  k)
    left = 0;  right = n - 1
    while (left < right) 
        x = a[k];  i = left;  j = right
        while (true) 
            while (a[i] < x); i += 1; end
            while (x < a[j]); j -= 1; end
            if (i > j); break; end
            t = a[i];  a[i] = a[j];  a[j] = t
            i += 1;  j -= 1
        end
        if (j < k); left  = i; end
        if (k < i); right = j; end
    end
    return a[k]
end

N = 10
a = []

for i in 0...N
    a[i] = rand * 100 + 1
    printf(" %d", a[i])
end
printf("\n")
begin 
    printf("小さい方から数えて何番目のものを求めますか? ")
    k = gets.to_i
end while (k < 1 || k > N)
printf("  %d番目 = %d\n", k, select(a, N, k - 1))

exit 0