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codeforces/19/19txt

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+A. Alternating Sum of Numbers
+time limit per test
+2 seconds
+memory limit per test
+256 megabytes
+input
+standard input
+output
+standard output
+You are given a sequence of integers. Output the alternating sum of this sequence. In other words, output a1−a2+a3−a4+a5−…
+a
+1
+−
+a
+2
++
+a
+3
+−
+a
+4
++
+a
+5
+−
+…
+. That is, the signs of plus and minus alternate, starting with a plus.
+
+Input
+The first line of the test contains one integer t
+t
+ (1≤t≤1000
+1
+≤
+t
+≤
+1000
+) — the number of test cases. Then follow t
+t
+ test cases.
+
+The first line of each test case contains one integer n
+n
+ (1≤n≤50
+1
+≤
+n
+≤
+50
+) — the length of the sequence. The second line of the test case contains n
+n
+ integers a1,a2,…,an
+a
+1
+,
+a
+2
+,
+…
+,
+a
+n
+ (1≤ai≤100
+1
+≤
+a
+i
+≤
+100
+).
+
+Output
+Output t
+t
+ lines. For each test case, output the required alternating sum of the numbers.
+
+Example
+Input
+Copy
+4
+4
+1 2 3 17
+1
+100
+2
+100 100
+5
+3 1 4 1 5
+Output
+Copy
+-15
+100
+0
+10