LeetCode--034--在排序数组中查找元素的第一个和最后一个位置（java）

给定一个按照升序排列的整数数组 nums，和一个目标值 target。找出给定目标值在数组中的开始位置和结束位置。

你的算法时间复杂度必须是 O(log n) 级别。

如果数组中不存在目标值，返回 [-1, -1]。

示例 1:

输入: nums = [5,7,7,8,8,10], target = 8
输出: [3,4]

示例 2:

输入: nums = [5,7,7,8,8,10], target = 6
输出: [-1,-1]

class Solution {
    public int[] searchRange(int[] nums, int target) {
        if(nums == null || nums.length == 0)return new int[]{-1,-1};
        return new int[]{findFirst(nums,target),findLast(nums,target)};
    }
    public int findFirst(int[] nums,int target){
        int start = 0;
        int end = nums.length - 1;
        while(start + 1 < end){
            int mid = (end - start) / 2 + start;
            if(nums[mid] < target){
                start = mid;
            }else{
                end = mid;
            }
        }
        if(nums[start] == target) return start;
        if(nums[end] == target) return end;
        return -1;
    }
    public int findLast(int[] nums,int target){
        int start = 0;
        int end = nums.length - 1;
        while(start + 1 < end){
            int mid = (end - start) / 2 + start;
            if(nums[mid] > target){
                end = mid;
            }else{
                start = mid;
            }
        }
        if(nums[end] == target) return end;
        if(nums[start] == target) return start;  
        return -1;
    }
    
}

方法2：(unpassed) 长度小于3会有错误

class Solution {
    public int[] searchRange(int[] nums, int target) {
        if(nums == null || nums.length == 0)return new int[]{-1,-1};
        if(nums.length == 1 && nums[0] == target) return new int[]{0,0};
        int start = 0,end = nums.length -1;
        boolean flag = false;
        while(start+1<end ){
            int mid = (end - start) / 2  + start;
            if(nums[mid] < target){
                start = mid;
            }else if(nums[mid] > target){
                end = mid;
            }else{
                flag = true;
                start = mid;
                end = mid;
                while(start >= 0 && nums[start] == target){
                    start--;
                }
                while(end < nums.length && nums[end] == target){
                    end++;
                }
                start++;
                end--;
                break;
            }
        }
        if(flag == true){
            return new int[]{start,end};
        }
        return new int[]{-1,-1};
    }
    
    
}

2019-04-27 19:51:51