二分法常用模板

1. java 二分法源代码采用的方法（ Arrays.binarySearch() ）
   ```
   public static int binarySearch1(int[] nums, int target){
   int left = 0;
   int right = nums.length -1; // [ left, right ]
   while (left <= right){ // left <= right
   int mid = (right - left) / 2 + left;
   if(nums[mid] > target){ // [ left, mid -1 ]

      right = mid - 1;
      } else if (nums[mid] < target ){   // [ mid + 1, right ]
      left = mid +1;
      } else {
      return mid;
      }

   return -1;
   }
2. leetcode见到的二分法

public class Solution {
    /**
    * @param A an integer array sorted in ascending order
    * @param target an integer
    * @return an integer
    */
    public int findPosition(int[] nums, int target) {
        if (nums == null || nums.length == 0) {
            return -1;
        }
        int start = 0, end = nums.length - 1;
        while (start + 1 < end) {//这里最关键：保证进入while循环的必须是至少有三个数。
            int mid = start + (end - start) / 2;
            if (nums[mid] == target) {
                return mid;
            } else if (nums[mid] < target) { //这里保证的是返回第一个相同值。
                start = mid;
            } else {
                end = mid;
            }
        }
        return -1;
    }
}