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Author: assassint2017

Count Primes/Count_Primes.cpp

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+// 附参考链接
+https://leetcode.com/problems/count-primes/discuss/?currentPage=1&orderBy=most_votes&query=
+https://assets.leetcode.com/static_assets/public/images/solutions/Sieve_of_Eratosthenes_animation.gif
+
+
+class Solution 
+{
+public:
+    int countPrimes(int n) 
+    {
+        // 边界条件处理
+        if (n < 2) return 0;
+
+        vector<bool> memo(n, true);
+        memo[0] = false;
+        memo[1] = false;
+
+        for (int i = 2; i <= sqrt(n); ++i)
+            if (memo[i])
+                for (int j = 2; i * j < n; ++j)
+                    memo[i * j] = false;
+        
+        int res = 0;
+        for (auto item : memo)
+            if (item)
+                ++res;
+        return res;
+    }
+};