二分查适用于单调区间， 三分查找则要求区间内为凸函数，即只有一个极值，三分查找用于查找极值。

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
public class Ternary {
   final static double EPS = 1e-10;

   public static void main(String[] args) {
      System.out.println(ternarySearch(1,10, a -> Math.pow(a-3,2), EPS));
   }

   interface MathOperation {
      double operation(double a);
   }

   public static double ternarySearch(double begin , double end, 
                                      MathOperation func, double eps){
      double mid1, mid2;
      while(begin + eps < end){
         mid1 = (begin + end) / 2;
         mid2 = (end + mid1) / 2;
         double res1 = func.operation(mid1);
         double res2 = func.operation(mid2);
         if(res1 > res2){
            begin = mid1;
         } else {
            end = mid2;
         }
      }
      return begin;
   }
}