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【Leetcode】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.
思路:因为是有序序列的变种,可以考虑应用二分查找。有两种分类讨论方式,一种是根据A[middle]与target的值比较进行讨论;一种是根据找出序列中的递增序列然后继续讨论。
代码一:
class Solution { public: int search(int A[], int n, int target) { if(n <= 0) return -1; int left = 0; int right = n - 1; int middle = 0; while(left <= right) { middle = (left + right) / 2; if(A[middle] == target) return middle; else if(A[middle] < target) { if(A[left] >= A[middle] && A[right] < target) right = middle - 1; else left = middle + 1; } else { if(A[right] <= A[middle] && A[left] > target) left = middle + 1; else right = middle - 1; } } return -1; } };
代码二:
class Solution { public: int search(int A[], int n, int target) { if(n <= 0) return -1; int left = 0; int right = n - 1; int middle = 0; while(left <= right) { middle = (left + right) / 2; if(A[middle] == target) return middle; if(A[left] <= A[middle]) { if(A[left] <= target && target < A[middle]) right = middle - 1; else left = middle + 1; } else { if(A[middle] < target && target <= A[right]) left = middle + 1; else right = middle - 1; } } return -1; } };
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