Search in Rotated Sorted Array

IIcyZhao

于 2013-06-14 18:49:57 发布

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分类专栏： LeetCode记录

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本文介绍了一种在未知旋转点的已排序数组中查找特定目标值的算法。该算法通过判断数组首元素与目标值的关系来确定搜索范围，并利用迭代方式在可能的区间内查找目标值。假设数组中没有重复元素。

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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.

class Solution {
public:
    int search(int A[], int n, int target) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if (A[0] == target) {
            return 0;
        } else if (A[0] > target) {
            if (A[n-1] == target) {
                return n-1;
            }
            for (int i = n-2; i > 0 && A[i] < A[i+1]; --i) {
                if (A[i] == target) {
                    return i;
                }
            }
        } else {
            for (int i = 1; i < n && A[i-1] < A[i]; ++i) {
                if (A[i] == target) {
                    return i;
                }
            }
        }
        return -1;
    }
};