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每日一记--2014.9.13

2024-07-22 11:00:05   225人阅读

今天贴三个小程序，程序很小，但是希望这些小东西都能记在心里

1.求多项式

 1 package 多项式; 2  3 public class Polynomial { 4  5     public static void main(String[] args) { 6         // TODO Auto-generated method stub 7         int[] xishu = new int[]{2,1,0,8,4}; 8         System.out.println(poly(xishu,3)); 9         10     }11     private static long poly(int[] xishu,int x){12         long po = 0L;13         for(int i = xishu.length-1;i>=0;i--){14             po=po*x+xishu[i];//注意系数是从an开始递减到a1的15         }    16         return po;17     }18 19 }

2.判断一个数是否为素数

 1 package 判断素数; 2  3 public class PrimeNumber { 4  5     public static void main(String[] args) { 6         // TODO Auto-generated method stub 7         System.out.println(isPrime(71)); 8     } 9 10     private static boolean isPrime(int a) {11         if(a<2){12             return false;13         }14         else{15             for(int i=2;i<Math.sqrt(a);i++){16                 if(a%i==0)17                     return false;18             }19         }20         return true;21     }22 23 }

3. 二分查找 

   时间复杂度为o(logN)

 1 package binarySearch; 2 //折半查找必须针对已排序的数列 3 public class BinarySearch { 4  5     static int NOT_FOUND = -1; 6     public static void main(String[] args) { 7         // TODO Auto-generated method stub 8         int[] aa = new int[]{2,3,7,89,100,256,445,789}; 9         System.out.println(binarySearch(aa,100));10     }11     private static int binarySearch(int[] sortedArray ,int find){12         int low =0;13         int high = sortedArray.length-1;14         while(low<=high){15             int mid = (low+high)/2;16             if(sortedArray[mid]<find){17                 low=mid+1;18             }19             else if(sortedArray[mid]>find){20                 high=mid-1;21             }22             else23                 return mid;24         }25         return NOT_FOUND;26     }27 28 }

 

每日一记--2014.9.13


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