Write a function to find the longest common prefix string amongst an array of strings.
func longestCommonPrefix(strs []string) string {
if(len(strs)==0){
return ""
}
var length int=1<<32 - 1
for i:=0;i<len(strs);i++{
if len(strs[i])<length{
length=len(strs[i])
}
}
var ret string
for j:=0;j<length;j++{
i:=0
for ;i<len(strs);i++{
if strs[i][j]!=strs[0][j]{
return ret
}
}
ret+=string(strs[0][j])
}
return ret
}