{"problem":{"name":"[蓝桥杯 2022 省 A] 求和","description":{"content":"给定 $n$ 个整数 $a_{1}, a_{2}, \\cdots, a_{n}$, 求它们两两相乘再相加的和，即 $$ S=a_{1} \\cdot a_{2}+a_{1} \\cdot a_{3}+\\cdots+a_{1} \\cdot a_{n}+a_{2} \\cdot a_{3}+\\cdots+a_{n-2} \\cdot a_{n-1}+a_{n-2} \\cdot a_{n}+a_{n-1} \\","description_type":"Markdown"},"platform":"Luogu","limit":{"time_limit":1000,"memory_limit":131072},"difficulty":{"LuoguStyle":"P2"},"is_remote":true,"is_sync":true,"sync_url":null,"sign":"LGP8772"},"statements":[{"statement_type":"Markdown","content":"给定 $n$ 个整数 $a_{1}, a_{2}, \\cdots, a_{n}$, 求它们两两相乘再相加的和，即\n\n$$\nS=a_{1} \\cdot a_{2}+a_{1} \\cdot a_{3}+\\cdots+a_{1} \\cdot a_{n}+a_{2} \\cdot a_{3}+\\cdots+a_{n-2} \\cdot a_{n-1}+a_{n-2} \\cdot a_{n}+a_{n-1} \\cdot a_{n}\n$$\n\n## Input\n\n输入的第一行包含一个整数 $n$ 。\n\n第二行包含 $n$ 个整数 $a_{1}, a_{2}, \\cdots a_{n}$ 。\n\n## Output\n\n输出一个整数 $S$，表示所求的和。请使用合适的数据类型进行运算。\n\n[samples]\n\n## Note\n\n对于 $30 \\%$ 的数据, $1 \\leq n \\leq 1000,1 \\leq a_{i} \\leq 100$ 。\n\n对于所有评测用例, $1 \\leq n \\leq 2\\times10^5,1 \\leq a_{i} \\leq 1000$ 。 \n\n蓝桥杯 2022 省赛 A 组 C 题。","is_translate":false,"language":"English"}],"meta":{"iden":"LGP8772","tags":["2022","前缀和","差分","蓝桥杯省赛"],"sample_group":[["4\n1 3 6 9","117"]],"created_at":"2026-03-03 11:09:25"}}