[leetcode]Search for a Range

最新推荐文章于 2018-09-05 14:58:19 发布

原创最新推荐文章于 2018-09-05 14:58:19 发布 · 238 阅读

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本文详细介绍了两种方法来解决在已排序数组中查找特定值的索引问题，并通过C++代码实现展示了这些方法的运用。通过逐步分析，读者将深入理解如何高效地定位目标值在数组中的位置。

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#include<iostream>
#include<vector>
using namespace std;
class Solution1
{
public:
    vector<int> findindex(vector<int>a,int target)
    {
        vector<int>res;
        int first=0,last=a.size()-1;
        while(first<last-1)
        {
            int mid=first+(last-first)/2;
            if(a[mid]<target)
                first=mid;
            else 
                last=mid;
        }
        if(a[first]==target)
            res.push_back(first);
        else if(a[last]==target)
            res.push_back(last);
        else
            res.push_back(-1);
        first=0,last=a.size()-1;
        while(first<last-1)
        {
            int mid=first+(last-first)/2;
            if(a[mid]<=target)
                first=mid;
            else 
                last=mid;
        }
        if(a[first]==target)
            res.push_back(first);
        else if(a[last]==target)
            res.push_back(last);
        else
            res.push_back(-1);
        return res;
    }
};

class Solution2
{
public:
    Solution2():first(-1),last(-1){}
    vector<int> findindex(vector<int>a,int target)
    {
        vector<int>res;
        search(a,0,a.size()-1,target);
        res.push_back(first);
        res.push_back(last);
        return res;
    }
    void search(vector<int>a,int l,int r,int target)
    {
        if(l>r)
            return;
        int mid=l+(r-l)/2;
        if(a[mid]==target)
        {
            if(first==-1)
                first=mid;
            else
                first=min(first,mid);
            last=max(last,mid); 
            search(a,l,mid-1,target);
            search(a,mid+1,r,target);
        }
        else if(a[mid]<target)
        {
            search(a,mid+1,r,target);
        }
        else
        {
            search(a,l,mid-1,target);
        }
    }
private:
    int first,last;
};
void main()
{
    Solution2 solution;
    int a[]={1,5,5,5,8,14};
    vector<int>arr(a,a+6);
    vector<int>result;
    result=solution.findindex(arr,5);
    for(auto i:result)
        cout<<i<<endl;
}