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    "https://leetcode.com/problems/random-pick-index\n",
    "\n",
    "\n",
    "Runtime: 160 ms, faster than 35.07% of C++ online submissions for Random Pick Index.\n",
    "Memory Usage: 53.7 MB, less than 11.58% of C++ online submissions for Random Pick Index.\n",
    "\n",
    "\n",
    "```cpp\n",
    "#include <vector>\n",
    "#include <algorithm>\n",
    "#include <string>\n",
    "#include <map>\n",
    "#include <vector>\n",
    "\n",
    "using namespace std;\n",
    "\n",
    "class Solution {\n",
    "public:\n",
    "    map<int, vector<int>> d;\n",
    "    Solution(vector<int>& nums) {\n",
    "        for (int i=0; i<nums.size(); i++) {\n",
    "            const auto v = nums[i];\n",
    "            if (d.find(v) == d.end()) {\n",
    "                //d.insert(vector<int> {i});\n",
    "                d[v].push_back(i);\n",
    "            } else {\n",
    "                d[v].push_back(i);\n",
    "            }\n",
    "        }\n",
    "    }\n",
    "    \n",
    "    int pick(int target) {\n",
    "        //6:45\n",
    "        return d[target][rand() % d[target].size()]; \n",
    "        //6:52\n",
    "    }\n",
    "};\n",
    "```"
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