【优选算法】专题三:二分查找 --- 34. 在排序数组中查找元素的第一个和最后一个位置

class Solution {
    public int[] searchRange(int[] nums, int target) {
        // 判断数组为空的情况下返回-1,-1
        int[] ret = new int[2];
        ret[0] = ret[1] = -1;
        if (nums.length == 0) return ret;

        // 判断左端点
        int left = 0,right = nums.length -1;
        while(left < right){
            int mid = left+(right-left)/2;
            if(nums[mid] < target) left = mid + 1;
            else right = mid;
        }
        // 判断是否有结果
        if(nums[left] != target) return ret;
        else ret[0] = left;

        // 判断右端点
        left = 0;right = nums.length -1 ;
        while(left < right){
            int mid = left+(right-left+1)/2;
            if(nums[mid] <= target) left = mid;
            else right = mid -1;
        }

        ret[1] = left;

        return ret;
    }
}