Find Minimum in rotated Sorted Array II

Catalogue:array-Division and Treatment method

Question

Suppose a sorted array is rotated on some pivot unknown to you beforehand.
(i.e., 0 1 2 4 5 6 7 might become 4 5 6 7 0 1 2).
Find the minimum element.
The array may contain duplicates.

First try

Class Solution {public:    int findmin (vector<int> &num) {        ret = 0;        BinarySearch (Num,0,num.size ()-1);        return Num[ret];    }        void BinarySearch (vector<int> &num, int start, int end)    {        if (end-start<=1)        {            if (num[end ]>num[start]) return;            else            {                ret = end;                return;            }        }                int mid = (start + end) >> 1;        if (Num[start]>num[mid])          binarysearch (num, start, mid);        else if (Num[mid+1]>num[end])          binarysearch (num, mid+1, end);        else if (num[mid]>num[mid+1])          ret = mid+1;    } Private:    int ret;};

result:wrong!

Input:	[10,1,10,10,10]
Output:	10
Expected:	1

Second try

There are repeating elements that are ignored by the while loop

Class Solution {public:    int findmin (vector<int> &num) {        ret = 0;        BinarySearch (Num,0,num.size ()-1);        return Num[ret];    }        void BinarySearch (vector<int> &num, int start, int end)    {        if (end-start<=1)        {            if (num[end ]>num[start]) return;            else            {                ret = end;                return;            }        }                int mid = (start + end) >> 1;        while (Start!=mid && num[start] = = Num[mid])        {            mid--;        }        while (End!=mid && num[end] = = Num[mid])        {            mid++;        }        if (Num[start] > Num[mid])          binarysearch (num, start, mid);        else if (num[mid+1] >= num[end])          binarysearch (num, mid+1, end);        else if (num[mid]>num[mid+1])          ret = mid+1;    } Private:    int ret;};

Result:runtime Error

Last executed input:[3,1,1]

Third try

Always be aware of data cross-border checks

Class Solution {public:    int findmin (vector<int> &num) {        ret = 0;        BinarySearch (Num,0,num.size ()-1);        return Num[ret];    }        void BinarySearch (vector<int> &num, int start, int end)    {        if (end-start<=1)        {            if (num[end ]>num[start]) return;            else            {                ret = end;                return;            }        }                int mid = (start + end) >> 1;        int mid2 = mid;        while (Start!=mid2 && num[start] = = Num[mid2])        {            mid2--;        }        if (Num[start] > Num[mid2])          binarysearch (num, start, MID2);        else        {            Mid2 = mid;            while (End!=mid && num[end] = = Num[mid])            {                mid++;            }            if (Num[mid] > Num[end])                BinarySearch (num, mid, end);        }    } Private:    int ret;};

result:wrong!

Input: [3,3,1,3]
Output: 3
Expected: 1

Fourth try:

Because there are duplicates, it is possible that mid and start or end are the same, but before start (or end) and mid have gone through the increment to decrement.

Class Solution {Public:int findmin (vector<int> &num) {ret = 0;        BinarySearch (Num,0,num.size ()-1);    return Num[ret];            } void BinarySearch (vector<int> &num, int start, int end) {if (end-start<=1) {            if (Num[end]>num[start]) return;                else {ret = end;            Return        }} int mid1 = (start + end) >> 1;        int mid2 = MID1;        while (start!=mid1 && num[mid1] = = Num[mid1-1]) {mid1--;        } while (Start!=mid1 && num[start] = = Num[start+1]) {start++; } if (Num[start] > Num[mid1] | |          (Start!=mid1 && Num[start] > Num[mid1-1]))        BinarySearch (num, start, MID1);            else {while (End!=mid2 && num[mid2] = = Num[mid2+1]) {mid2++; } while (End!=mid2 && nuM[end] = = Num[end-1]) {end--; } if (Num[mid2] > Num[end] | |                (End!=mid2 && Num[mid2] > num[end-1]))        BinarySearch (num, mid2, end); }}private:int ret;};

result:accepted

Find Minimum in rotated Sorted Array II