PHP数组连续性判定?报错

现有一数组如下：

array(44) { 
[0]=> string(1) "1" 
[1]=> string(3) "1.1" 
[2]=> string(3) "1.2" 
[3]=> string(3) "1.3" 
[4]=> string(3) "1.6" 
[5]=> string(3) "1.5" 
[6]=> string(3) "1.7" 
[7]=> string(3) "1.8" 
[8]=> string(1) "2" 
[9]=> string(3) "2.1" 
[10]=> string(3) "2.2" 
[11]=> string(3) "2.3" 
[12]=> string(3) "2.4" 
[13]=> string(3) "2.5" 
[14]=> string(3) "2.6" 
[15]=> string(3) "2.7" 
[16]=> string(3) "2.8" 
[17]=> string(5) "2.8.1" 
[18]=> string(5) "2.8.2" 
[19]=> string(1) "3" 
[20]=> string(3) "3.1" 
[21]=> string(3) "3.2" 
[22]=> string(1) "4" 
[23]=> string(3) "4.1" 
[24]=> string(3) "4.2" 
[25]=> string(3) "4.3" 
[26]=> string(5) "4.3.1" 
[27]=> string(5) "4.3.2" 
[28]=> string(5) "4.3.3" 
[29]=> string(3) "4.4" 
[30]=> string(5) "4.4.1" 
[31]=> string(5) "4.4.2" 
[32]=> string(5) "4.4.3" 
[33]=> string(1) "5" 
[34]=> string(3) "5.1" 
[35]=> string(3) "5.2" 
[36]=> string(3) "5.3" 
[37]=> string(5) "5.3.1" 
[38]=> string(5) "5.3.2" 
[39]=> string(5) "5.3.3" 
[40]=> string(5) "5.3.4" 
[41]=> string(3) "5.4" 
[42]=> string(5) "5.4.1" 
[43]=> string(5) "5.4.2" 
}

有这样一个数组，我如何判定每个Value是连续的，比如上面没有1.4，则应该报错；同样，1.6和1.5顺序反了，也应该报错，求大神指教下啊！！！