[CareerCup][Google Interview] 找出现次数

Given a sorted array and a number n.How can u find the number of occurance of n in the array . should be o(logn)

http://www.careercup.com/question?id=8877058

改变一下二分查找的方法，一次找到最左边，另一次找到最右边。

#include <iostream>
#include <vector>
using namespace std;

int findPos(vector<int> &a, int left, int right, int key, bool findLeft)
{
    if (left > right)
        return -1;

    int mid = (left + right) / 2;

    if (a[mid] == key)
    {
        int pos = findLeft ? findPos(a, left, mid - 1, key, findLeft) : findPos(a, mid + 1, right, key, findLeft);
        return (pos == -1 ? mid : pos);
    }
    else if (a[mid] > key)
    {
        return findPos(a, left, mid - 1, key, findLeft);
    }
    else
    {
        return findPos(a, mid + 1, right, key, findLeft);
    }
}

int main()
{
    vector<int> a;
    for(int i = 0; i < 9; i++)
        for(int j = 0; j < 5; j++)
            a.push_back(i);

    int pos1 = findPos(a, 0, a.size() - 1, 5, true);
    int pos2 = findPos(a, 0, a.size() - 1, 5, false);

    cout << pos1 << ' ' << pos2 << endl;
}

转载于:https://www.cnblogs.com/chkkch/archive/2012/10/29/2744640.html