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