剑指offer 编程题（27）：数组中出现次数统计

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本文介绍了一种算法，用于从数组中找出出现次数超过数组长度一半的数字，并扩展到求解出现次数最多的数字及其计数，同时提供了使用C++实现的具体代码示例。

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题目描述

数组中有一个数字出现的次数超过数组长度的一半，请找出这个数字。例如输入一个长度为9的数组{1,2,3,2,2,2,5,4,2}。由于数字2在数组中出现了5次，超过数组长度的一半，因此输出2。如果不存在则输出0

class Solution {
public:
    int MoreThanHalfNum_Solution(vector<int> numbers) {
        if(numbers.size() == 0)
            return 0;

        map<int,int> countmap;
        int size = numbers.size()/2;

        for(int i=0; i<numbers.size(); ++i)
        {
            countmap[ numbers[i] ]++;
            if(countmap[ numbers[i] ] > size)
                return numbers[i];
        }

        return 0;
    }
};

扩展一：统计数组中出现次数最多的数字，返回最多次数。

class Solution {
public:
    int MoreThanHalfNum_Solution(vector<int> numbers) {
        if (numbers.size() == 0)
            return 0;
        int maxcount = 0;
        map<int, int> countmap;
        //int size = numbers.size() / 2;

        for (int i = 0; i < numbers.size(); ++i)
        {
            countmap[numbers[i]]++;
            if (countmap[numbers[i]] > maxcount)
                maxcount = countmap[numbers[i]];
        }

        return maxcount;
    }
};

扩展二：统计数组中出现次数最多的数字，返回最多次数的那个数字。

class Solution {
public:
    int MoreThanHalfNum_Solution(vector<int> numbers) {
        if (numbers.size() == 0)
            return 0;
        int maxcount = 0;
        int maxnumber = 0;
        map<int, int> countmap;
        //int size = numbers.size() / 2;

        for (int i = 0; i < numbers.size(); ++i)
        {
            countmap[numbers[i]]++;
            if (countmap[numbers[i]] > maxcount)
            {
                maxcount = countmap[numbers[i]];
                maxnumber = numbers[i];
            }
        }
        return maxnumber;
    }
};

扩展三：统计数组中出现次数，返回第二多次数的那个数字。

class Solution {
public:
    int MoreThanHalfNum_Solution(vector<int> numbers) {
        if (numbers.size() == 0)
            return 0;
        int maxcount = 0;
        int maxnumber = 0;
        int seccount = 0;
        int secnumber = 0;
        map<int, int> countmap;
        int size = numbers.size() / 2;
        for (int i = 0; i < numbers.size(); ++i)
        {
            countmap[numbers[i]]++;
        }
        for (int i = 0; i < numbers.size(); ++i)
        {
            if (countmap[numbers[i]] > maxcount)
            {
                seccount = maxcount;
                secnumber = maxnumber;
                maxcount = countmap[numbers[i]];
                maxnumber = numbers[i];
            }
            else if(countmap[numbers[i]] > seccount && countmap[numbers[i]] <= maxcount)
            {
                seccount = countmap[numbers[i]];
                secnumber = numbers[i];
            }
        }
        cout << "最多次数的数字是：" << maxnumber << "出现了" << maxcount << "次"<<endl;
        cout<< "第二多次数是：" << secnumber << "出现了" << seccount << "次" << endl;
        return secnumber;
    }
};

扩展四：统计字符串中出现次数，返回出现最多次数的那个字符。‘

#include<iostream>  
#include<string>  
#include<stdlib.h>

using namespace std;
int main()
{
    string str;
    cout << "input some text:" << endl;
    getline(cin, str);
    int maxcount = 0;
    string maxstring;

    int cnt[256] = {};
    for (int i = 0; i<str.size(); i++)

        cnt[(int)str[i]]++;
    for (int i = 0; i<256; i++)//输出字符出现次数  
    {
        if (cnt[i] != 0)
            cout << (char)i << ':' << cnt[i] << endl;
        if (cnt[i] > maxcount)
        {
            maxcount = cnt[i];
            maxstring = (char)i;
        }
    }
    cout <<"出现次数最多的字符是"<< maxstring << "出现了"<<maxcount<<"次" << endl;
    system("pause");
}

class Solution {
public:
    string MoreThanHalfNum_Solution(string str) 
    {
        int maxcount = 0;
        string maxstring;

        int cnt[256] = {};
        for (int i = 0; i<str.size(); i++)

            cnt[(int)str[i]]++;
        for (int i = 0; i<256; i++)//输出字符出现次数  
        {
            if (cnt[i] != 0)
                cout << (char)i << ':' << cnt[i] << endl;
            if (cnt[i] > maxcount)
            {
                maxcount = cnt[i];
                maxstring = (char)i;
            }
        }
        cout << "出现次数最多的字符是" << maxstring << "出现了" << maxcount << "次" << endl;
        return maxstring;
    }
};

#define _CRT_SECURE_NO_WARNINGS 1  
#include<stdio.h>  
#include<stdlib.h>  
#include<assert.h>  
#include<string>
#include<iostream>
#include<vector>
#include<map>
using namespace std;
class Solution {
public:
    string MoreThanHalfNum_Solution(string str) 
    {
        int maxcount = 0;
        string maxstring;

        map<char, int> cnt;
        for (int i = 0; i<str.size(); i++)

            cnt[str[i]]++;
        for (int i = 0; i<cnt.size(); i++)//输出字符出现次数  
        {
            if (cnt[i] != 0)
                cout << (char)i << ':' << cnt[i] << endl;
            if (cnt[i] > maxcount)
            {
                maxcount = cnt[i];
                maxstring = (char)i;
            }
        }
        cout << "出现次数最多的字符是" << maxstring << "出现了" << maxcount << "次" << endl;
        return maxstring;
    }
};
int main()
{
    string b = "aaaaaabbbbbbbbbccccddddddddddddddddddddd";
    Solution s;
    string count;
    count = s.MoreThanHalfNum_Solution(b);
    cout << count << endl;

    system("pause");
    return 0;
}