{"trustable":true,"prependHtml":"\u003cstyle type\u003d\u0027text/css\u0027\u003e\n .input, .output {\n border: 1px solid #888888;\n }\n .output {\n margin-bottom: 1em;\n position: relative;\n top: -1px;\n }\n .output pre, .input pre {\n background-color: #EFEFEF;\n line-height: 1.25em;\n margin: 0;\n padding: 0.25em;\n }\n \u003c/style\u003e\n \u003clink rel\u003d\"stylesheet\" href\u003d\"//codeforces.org/s/96598/css/problem-statement.css\" type\u003d\"text/css\" /\u003e\u003cscript\u003e window.katexOptions \u003d { disable: true }; \u003c/script\u003e\n\u003cscript type\u003d\"text/x-mathjax-config\"\u003e\n MathJax.Hub.Config({\n tex2jax: {\n inlineMath: [[\u0027$$$\u0027,\u0027$$$\u0027], [\u0027$\u0027,\u0027$\u0027]],\n displayMath: [[\u0027$$$$$$\u0027,\u0027$$$$$$\u0027], [\u0027$$\u0027,\u0027$$\u0027]]\n }\n });\n\u003c/script\u003e\n\u003cscript type\u003d\"text/javascript\" async src\u003d\"https://mathjax.codeforces.org/MathJax.js?config\u003dTeX-AMS_HTML-full\"\u003e\u003c/script\u003e","sections":[{"title":"","value":{"format":"HTML","content":"\u003cp\u003eEvery day a new programming problem is published on Codehorses. Thus, $$$n$$$ problems will be published in the following $$$n$$$ days: the difficulty of the $$$i$$$-th problem is $$$a_i$$$.\u003c/p\u003e\u003cp\u003ePolycarp wants to choose exactly three days $$$i$$$, $$$j$$$ and $$$k$$$ ($$$i \u0026lt; j \u0026lt; k$$$) so that the difference of difficulties on the day $$$j$$$ and the day $$$i$$$ is equal to the difference of difficulties on the day $$$k$$$ and day $$$j$$$. In other words, Polycarp wants equality $$$a_j-a_i\u003da_k-a_j$$$ to be true.\u003c/p\u003e\u003cp\u003eDetermine the number of possible ways for Polycarp to choose the three days in the desired way.\u003c/p\u003e"}},{"title":"Input","value":{"format":"HTML","content":"\u003cp\u003eThe first line contains an integer $$$t$$$\u0026nbsp;— the number of test cases in the input ($$$1 \\le t \\le 10$$$). Then $$$t$$$ test case descriptions follow.\u003c/p\u003e\u003cp\u003eThe first line of a test case contains an integer $$$n$$$\u0026nbsp;— the number of the days ($$$3 \\le n \\le 2000$$$).\u003c/p\u003e\u003cp\u003eThe second line of the test case contains $$$n$$$ integers $$$a_1, a_2, \\dots, a_n$$$, where $$$a_i$$$ is the difficulty of the problem on the $$$i$$$-th day ($$$1 \\le a_i \\le 10^9$$$).\u003c/p\u003e"}},{"title":"Output","value":{"format":"HTML","content":"\u003cp\u003eOutput $$$t$$$ integers\u0026nbsp;— the answers for each of the test cases in the input, in the order they are given. The answer to a test case is the number of triples of indices $$$i$$$, $$$j$$$, and $$$k$$$ such that $$$1 \\le i \u0026lt; j \u0026lt; k \\le n$$$ and $$$a_k-a_j\u003da_j-a_i$$$.\u003c/p\u003e"}},{"title":"Examples","value":{"format":"HTML","content":"\u003ctable class\u003d\u0027vjudge_sample\u0027\u003e\n\u003cthead\u003e\n \u003ctr\u003e\n \u003cth\u003eInput\u003c/th\u003e\n \u003cth\u003eOutput\u003c/th\u003e\n \u003c/tr\u003e\n\u003c/thead\u003e\n\u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd\u003e\u003cpre\u003e4\n5\n1 2 1 2 1\n3\n30 20 10\n5\n1 2 2 3 4\n9\n3 1 4 1 5 9 2 6 5\n\u003c/pre\u003e\u003c/td\u003e\n \u003ctd\u003e\u003cpre\u003e1\n1\n4\n5\n\u003c/pre\u003e\u003c/td\u003e\n \u003c/tr\u003e\n\u003c/tbody\u003e\n\u003c/table\u003e\n"}}]}