Chef and Favourite Sequence
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Read problems statements in Mandarin Chinese and Russian.
Chef has an integer sequence a1, a2, ..., aN of size N, where all the elements of the sequence are 0 initially. Chef also has M segments, here the ith one is [Li, Ri]. He wants to create new sequences using the following operation:
- In a single operation, he picks a segment from the M segments. Let the chosen segment be [s, t].
- Then flip the all elements from sth to tth elements, namely, ai is changed to 1 − ai for all s ≤ i ≤ t.
Chef can perform the operation as many times as Chef likes. Chef wants to know how many different sequences Chef can make. Since the answer can be very large, please print it modulo 1000000007 (109+7).
The first line contains two space-separated integers N and M, denoting the size of the sequence and the number of the segments respectively. Then the ith line of the next M lines contains two space-separated integers Li and Ri, denoting the ith segments.
Print a single line containing one integer, denoting the number of the sequences which can be created by Chef, modulo 1000000007 (109+7).
- 1 ≤ N, M ≤ 100000 (105)
- 1 ≤ Li ≤ Ri ≤ N
Input: 3 3 1 1 2 2 3 3 Output: 8
In the example case, all the sequences (0,0,0), (0,0,1), (0,1,0), (1,0,0), (0,1,1), (1,0,1), (1,1,0), (1,1,1) can be created by Chef.
|Tags||easy-medium, feb14, furko|
|Time Limit:||1 sec|
|Source Limit:||50000 Bytes|
|Languages:||C, CPP14, JAVA, PYTH, PYTH 3.5, CS2, PAS fpc, PAS gpc, RUBY, PHP, GO, NODEJS, HASK, SCALA, D, PERL, FORT, WSPC, ADA, CAML, ICK, BF, ASM, CLPS, PRLG, ICON, SCM qobi, PIKE, ST, NICE, LUA, BASH, NEM, LISP sbcl, LISP clisp, SCM guile, JS, ERL, TCL, PERL6, TEXT, CLOJ, FS|
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