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public class Solution {   
    public int[] searchRange(int[] nums, int target) {
        int[] range = {nums.length - 1, -1}; // {6, -1}
        helper(nums, target, 0 , nums.length - 1, range);
        if(range[0] > range[1]){
            range[0] = -1;
        }
        return range;
    }
  
    public void helper(int[] nums, int target, int start, int end, int[] range){
        if(start > end){
            return;
        }
        int mid = start + (end - start)/2; 
        if(nums[mid] == target){ 
            if(mid < range[0]){
                range[0] = mid; 
                helper(nums, target, start, mid - 1, range);
            }
            if(mid > range[1]){
                range[1] = mid; 
                helper(nums, target, mid + 1, end, range); // 5, 5
            }
        } else if(nums[mid] < target){
            helper(nums, target, mid + 1, end, range);
        } else{
            helper(nums, target, start, mid - 1, range);
        }
    }
}

public class Solution {
    public int[] searchRange(int[] nums, int target) {
        int[] res = new int[2];
        Arrays.fill(res, -1);
        if (nums == null || nums.length < 1) return res;
        int len = nums.length;
        int i = 0;
        int j = len - 1;
        while (i < j) {
            int mid = i + (j - i) / 2;
            if (nums[mid] < target) {
                i = mid + 1;
            } else {
                j = mid;
            }
        }
        if (nums[i] != target) return res;
        else res[0] = i;
        
        j = len - 1;
        while (i < j) {
            int mid = i + (j - i) / 2 + 1;
            /*
            Consider the following case:
            [5 7], target = 5
            Now A[mid] = 5, then according to rule 2, we set i = mid. 
            This practically does nothing because i is already equal to mid. As a result, the search range is not moved at all!
            The solution is by using a small trick: instead of calculating mid as mid = (i+j)/2, we now do:
            mid = (i+j)/2+1
            */
            if (nums[mid] > target) {
                j = mid - 1;
            } else {
                i = mid;
            }
        }
        res[1] = j;
        return res;
    }
}