标签：style blog class code c java
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.
Have you been asked this question in an interview?
二分查找。
1. 如果A[mid]>A[l]，也就是A[l...mid]是递增序。如果target>=A[l]&&target<A[mid]，那么target只可能在[l...mid-1]这个区间上，否则在[mid+1...h]这个区间。
2. 如果A[mid]<=A[l],那么A[mid...h]是递增序。如果target>A[mid] && target<=A[h]，那么target只可能在[mid+1...h]这个区间，否则在[l...mid-1]这个区间。
1 class Solution { 2 public: 3 int search(int A[], int n, int target) { 4 if (n == 0) return -1; 5 int l = 0, h = n - 1, mid; 6 7 while (l <= h) { 8 mid = (l + h) / 2; 9 if (A[mid] == target) return mid; 10 if (A[mid] >= A[l]) { 11 if (target >= A[l] && target < A[mid]) { 12 h = mid - 1; 13 } else { 14 l = mid + 1; 15 } 16 } else { 17 if (target > A[mid] && target <= A[h]) { 18 l = mid + 1; 19 } else { 20 h = mid - 1; 21 } 22 } 23 } 24 25 return -1; 26 } 27 };
Follow up for "Search in Rotated Sorted Array":
What if duplicates are
allowed?
Would this affect the run-time complexity? How and why?
Write a function to determine if a given target is in the array.
有了重复数。那么前面的情况，只对应于A[mid]>A[l]和A[mid]<A[l]是成立的。对于A[mid]==A[l]，我们无法确定该数是在左区间还是右区间，反正一定不会是在A[l]上，所以l++。
最坏情况就是整个数组都是同一个数，target不在数组中，这样每次都只能l++，算法复杂度是O(n)。
1 class Solution { 2 public: 3 bool search(int A[], int n, int target) { 4 if (n == 0) return false; 5 int l = 0, h = n - 1, mid; 6 7 while (l <= h) { 8 mid = (l + h) / 2; 9 if (A[mid] == target) return true; 10 if (A[mid] == A[l]) { 11 l++; 12 } else if (A[mid] > A[l]) { 13 if (target >= A[l] && target < A[mid]) { 14 h = mid - 1; 15 } else { 16 l = mid + 1; 17 } 18 } else { 19 if (target > A[mid] && target <= A[h]) { 20 l = mid + 1; 21 } else { 22 h = mid - 1; 23 } 24 } 25 } 26 27 return false; 28 } 29 };
Leetcode | Search in Rotated Sorted Array I & II,布布扣,bubuko.com
Leetcode | Search in Rotated Sorted Array I & II
标签：style blog class code c java
原文地址：http://www.cnblogs.com/linyx/p/3735551.html
