自渡的博客

Generally speaking, there are a lot of problems about strings processing. Now you encounter another such problem. If you get two strings, such as “asdf” and “sdfg”, the result of the addition between ...

某人有N袋金币，其中第i袋内金币的数量是Ai。现在他决定选出2袋金币送给小Hi，再选2袋金币送给小Ho，同时使得小Hi和小Ho得到的金币总数相等。他想知道一共有多少种不同的选择方法。 具体来说，有多少种下标四元组(i, j, p, q)满足i, j, p, q两两不同，并且i < j, p < q, Ai+ Aj= Ap+ Aq。 例如对于数组A=[1, 1, 2, 2, ...