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【LeetCode】Search in Rotated Sorted Array (3 solutions)
Search in Rotated Sorted Array
Suppose a sorted array 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).
You are given a target value to search. If found in the array return its index, otherwise return -1.
You may assume no duplicate exists in the array.
解法一：顺序查找
class Solution {public: int search(int A[], int n, int target) { for(int i = 0; i < n; i ++) { if(A[i] == target) return i; } return -1; }};
解法二：二分查找
先用二分法找到最大元素，将数组切分成有序数组，再进行二分查找
class Solution {public: int search(int A[], int n, int target) { if(n==1) return (target==A[0])?0:-1; //find the maximum first int low = 0; int high = n-1; while(low < high) { int mid = (low+high)/2; if(A[mid] < A[low]) high = mid-1; else if(A[mid] > A[low]) low = mid; else {//low+1==high if(A[high]>A[low]) low = high; break; } } int ind = low; //to here, low is the index of maximum //0~ind, ind+1~n-1 are two sorted arrays if(target >= A[0]) {//first array: 0~ind low = 0; high = ind; while(low <= high) { int mid = (low+high)/2; if(target == A[mid]) return mid; else if(target > A[mid]) low = mid+1; else high = mid-1; } return -1; } else {//second array: ind+1, n-1 low = ind+1; high = n-1; while(low <= high) { int mid = (low+high)/2; if(target == A[mid]) return mid; else if(target > A[mid]) low = mid+1; else high = mid-1; } return -1; } }};
解法三：可处理重复元素的二分查找
class Solution {public: int search(int A[], int n, int target) { int low = 0; int high = n-1; while (low <= high) { int mid = (low+high)/2; if(A[mid] == target) return mid; if (A[low] < A[mid]) { if(A[low] <= target && target < A[mid]) //binary search in sorted A[low~mid-1] high = mid - 1; else //subproblem from low to high low = mid + 1; } else if(A[mid] < A[high]) { if(A[mid] < target && target <= A[high]) //binary search in sorted A[mid+1~high] low = mid + 1; else //subproblem from low to mid-1 high = mid - 1; } else if(A[low] == A[mid]) low += 1; //A[low]==A[mid] is not the target, so remove it else if(A[mid] == A[high]) high -= 1; //A[high]==A[mid] is not the target, so remove it } return -1; }};
【LeetCode】Search in Rotated Sorted Array (3 solutions)
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