java 算法二分查找和折半查找

 java 算法二分查找与折半查找

折半查找 ：首先数组是已经排好序的

实例代码：

package com.hao.myrxjava;



public class HalfDivision {

  
  public static int halfDivision(int value, int[] array) {
    if (array == null || array.length == 0)
      throw new NullPointerException("array is null");
    int low = 0;
    int high = array.length - 1;
    int mid = (low+high)/2;
    while (array[mid] != value) {
      if (array[mid] > value)
 high = mid - 1;
      else
 low = mid + 1;
      if (low > high)
 return -1;
      mid = (low+high)/2;
      if (array[mid] == value)
 return mid;
    }
    return mid;
  }

  
  public static int halfDivision(int value, int[] array, int low, int high) {
    if (low > high)
      return -1;
    int mid = (low + high) / 2;
    if (array[mid] == value)
      return mid;
    else if (array[mid] > value)
      return halfDivision(value, array, low, mid - 1);
    else if (array[mid] < value)
      return halfDivision(value, array, mid+1, high);
    return -1;
  }
}

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