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  • Search in rotated array two

    description:

    Follow up for "Search in Rotated Sorted Array":
    What if duplicates are allowed?

    Would this affect the run-time complexity? How and why?

    Suppose an array sorted in ascending order is rotated at some pivot unknown to you beforehand.

    (i.e., 0 1 2 4 5 6 7 might become 4 5 6 7 0 1 2).

    Write a function to determine if a given target is in the array.

    The array may contain duplicates.

    Thoughts:

    1.按照写rotated sorteg array时的思路,我写这个问题的时候,在重新设置low和high的时候,跳过了和middle一样的重复部分。另外要注意的一个点就是当nums[low]和nums[high]相等的时候我们要重新设置low和high

    public boolean search(int[] nums, int target){
            int low = 0;
            int high = nums.length-1;
            if(nums[high] == nums[low]&&nums.length>2){
                for(int i = high-1;i>=low;i--){
                    if(nums[i] == nums[high]){
                        high--;
                    }
                }
            }
            while(low <= high){
                int middle = (low+high)/2;
                if(nums[middle] == target){
                    return true;
                }else if(nums[middle] >=nums[low]){
                    if(target>=nums[low] && target<nums[middle]){
                        for(int i = middle-1;i>=low;i--){
                            if(nums[i] == nums[middle]){
                                middle--;
                            }else{
                                break;
                            }
                        }
                        high = middle -1; 
                    }else{
                        for(int i = middle+1;i<=high;i++){
                            if(nums[i] == nums[middle]){
                                middle++;
                            }else{
                                break;
                            }
                        }
                        low = middle + 1;
                    }
                }else{
                    if(target>nums[middle]&&target<=nums[high]){
                        for(int i =middle+1;i<=high;i++){
                            if(nums[i] == nums[middle]){
                                middle++;
                            }else{
                                break;
                            }
                        
                        }
                        low = middle +1;
                    }else{
                        for(int i = middle-1;i>=low;i--){
                            if(nums[i] == nums[middle]){
                                middle--;
                            }else{
                                break;
                            }
                            
                        }
                        high = middle - 1;
                    }
                }
            }
            return false;
        }

    2.前面的解法,思路是清晰的过程是麻烦的,需要加很多的判断条件,为了避免这个问题,我们不讲middle和low进行比较,而是让它和high进行比较,这样就能够避免之前的nums[low]和nums[high]相等的情况,所带来的麻烦。

    public boolean search2(int[] nums, int target){
            if(nums.length == 0){
                return false;
            }
            int low = 0;
            int high = nums.length - 1;
            while(low < high){
                int middle = (low +high)/2;
                if(nums[middle] == target){
                    return true;
                }else{
                    if(nums[middle] < nums[high]){
                        if(target > nums[middle] && target <= nums[high]){
                            low = middle + 1;
                        }else{
                            high = middle - 1;
                        }
                    }else if(nums[middle] > nums[high]){
                        if(target >= nums[low] & target < nums[middle]){
                            high = middle -1;
                        }else{
                            low = middle +1;
                        }
                    }else{
                        high--;
                    }
                }
            }
            return nums[low]==target;
        }
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  • 原文地址:https://www.cnblogs.com/whatyouknow123/p/7509952.html
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