awk - print overlapping ranges

Question

I'm afraid I haven't come across a direct way of doing this, although I tried adapting some provided solutions for similar scenarios (but not quite for what I need). Given this data:

1118 1120
1121 1124
1122 1127
1125 1126
1128 1133
1130 1135
1136 1139
1137 1138
1140 1145

It is already sorted by column 1. Except for first and last lines, all the others have intervals that overlap, in pairs. So I want an output with just the overlapping ranges:

1122 1124
1125 1126
1130 1133
1137 1138

For me at least, this is harder that I expected at first glance.

Answer 1

Here's one way to do it in awk. There's likely a more efficient way.

awk '{b=e=0; for(i=$1; i<=$2; i++) { if (exists[i]) if(b==0) {b=e=i} else {e=i}; exists[i]=i; } if(b) print b,e; }' input_file