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- Count the number of prime numbers less than a non-negative number, n.
- Example:
- Input: 10
- Output: 4
- Explanation: There are 4 prime numbers less than 10, they are 2, 3, 5, 7.
复制代码
- class Solution {
- public int countPrimes(int n) {
- if(n <= 1) return 0;
-
- boolean[] arr = new boolean[n];
- arr[0] = true;
- arr[1] = true;
-
- for(int i = 2; i < Math.sqrt(n) ; i++){
- if(arr[i] == false){
-
- for(int j = 2 ; j*i < n; j++){
-
- arr[i*j] = true;
- }
- }
-
- }
- int count = 0;
-
- for(int i = 2; i< arr.length; i++){
-
- if(!arr[i]) count++;
- }
-
- return count;
- }
-
- }
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