168. Excel表列名称
public class Solution168 {
public String convertToTitle(int n) {
String restult = "";
while(n>0) {
n--;
restult =(char)('A'+(n%26))+restult;
n=n/26;
}
return restult;
}
public static void main(String[] args) {
// TODO Auto-generated method stub
Solution168 s = new Solution168();
System.err.println(s.convertToTitle(26));
System.err.println(s.convertToTitle(52));
System.err.println(s.convertToTitle(27));
System.err.println(s.convertToTitle(26));
System.err.println(s.convertToTitle(28));
System.err.println(s.convertToTitle(701));
}
}
204. 计数质数
public class Solution204 {
public int countPrimes(int n) {
int result = 0;
for (int i = 1; i < n; i++) {
if (isPrime(i)) {
result++;
}
}
return result;
}
/**
* AKS算法计算一个数是否是素数
* https://stackoverflow.com/questions/1801391/what-is-the-best-algorithm-for-checking-if-a-number-is-prime
* @param n
* @return
*/
public boolean isPrime(int n) {
if (n == 1) {
return false;
}
if (n == 2 || n == 3) {
return true;
}
if (n % 2 == 0 || n % 3 == 0) {
return false;
}
int i = 5, w = 2;
while (i * i <= n) {
if (n % i == 0) {
return false;
}
i += w;
w = 6 - w;
}
return true;
}
public static void main(String[] args) {
// TODO Auto-generated method stub
Solution204 s = new Solution204();
System.out.println(s.countPrimes(10));
}
}
179. 最大数
import java.util.ArrayList;
import java.util.Comparator;
import java.util.List;
public class Solution179 {
public String largestNumber(int[] nums) {
List<String> lists =new ArrayList<String>(nums.length);
for(int num:nums) {
lists.add(num+"");
}
lists.sort(new Comparator<String>() {
@Override
public int compare(String o1, String o2) {
// TODO Auto-generated method stub
return (o2+o1).compareTo(o1+o2);
}
});
if(lists.get(0).equals("0")) {
return "0";
}
StringBuffer sb = new StringBuffer();
for(String numStr:lists) {
sb.append(numStr);
}
return sb.toString();
}
public static void main(String[] args) {
// TODO Auto-generated method stub
Solution179 s = new Solution179();
int[] nums = new int[] {3,30,34,5,9};
System.out.println(s.largestNumber(nums));
}
}
这道题先思考清楚本质是一个排序问题，坑的地方在于0的处理上。