[LeetCode] Search in Rotated Sorted Array 解题报告
2016-01-12 11:08
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Suppose a sorted array is rotated at some pivot unknown to you beforehand.
(i.e.,
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.
» Solve this problem
[解题思想]
同样是二分,难度主要在于左右边界的确定。需要结合两个不等式:
1. A[m] ? A[left]
2. A[m] ? target
具体逻辑看code。
Update 08/23/2014
See the comments from reader. Add a graph and also change the code a bit for readability(See highlight code in red).
The general idea is, to use some in-equations to distinguish below 3 conditions, and decide the new range of binary search.
(i.e.,
0 1 2 4 5 6 7might 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.
» Solve this problem
[解题思想]
同样是二分,难度主要在于左右边界的确定。需要结合两个不等式:
1. A[m] ? A[left]
2. A[m] ? target
具体逻辑看code。
[code]1: int search(int A[], int n, int target) { 2: // Start typing your C/C++ solution below 3: // DO NOT write int main() function 4: int l = 0, r = n-1; 5: while(l<=r) 6: { 7: int m = (l+r)/2; 8: if(A[m] == target) return m; 9: if(A[m]>= A[l]) 10: { 11: if(A[l]<=target && target<= A[m]) 12: r=m-1; 13: else 14: l = m+1; 15: } 16: else 17: { 18: if(A[m] >= target || target>= A[l]) 19: r = m-1; 20: else 21: l = m+1; 22: } 23: } 24: return -1; 25: }
Update 08/23/2014
See the comments from reader. Add a graph and also change the code a bit for readability(See highlight code in red).
The general idea is, to use some in-equations to distinguish below 3 conditions, and decide the new range of binary search.
1: int search(int A[], int n, int target) { 2: int l = 0, r = n-1; 3: while(l<=r) 4: { 5: int m = (l+r)/2; 6: if(A[m] == target) return m; 7: if(A[m]>= A[l]) 8: { 9: if(A[l]<=target && target< A[m]) 10: r=m-1; 11: else 12: l = m+1; 13: } 14: else 15: {
16: if(A[m]< target && target<=A[r])
17: l = m+1; 18: else 19: r = m-1;
20: } 21: } 22: return -1; 23: }
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