例：

給定一段英語文字，要求對其中單詞出現的個數按照從小到大進行排序，出現次數相同的按照首字母順序排列。

演算法實現：

#include <iostream>
#include <algorithm>
#include <vector>
#include <unordered_map>
#include <map>
#include <fstream>

using namespace std;
typedef pair<string, int> PAIR;

int cmp(const PAIR &x, const
 
 PAIR &y) {
    return x.second < y.second;
}

int main() {
    string file;
    cout << "Enter the text path:";
    cin >> file;
    ifstream inout;
    inout.open(file, ios::in);

    if (inout.fail()) {
        cout << "Your file don't exist!" << endl;
        return
 
 0;
    }
    vector<string> key;
    map<string, int> map;
    string skey;
    int flag = 0;
    inout >> skey;
    key.push_back(skey);
    map[skey] = 1;
    while (!inout.eof()) {
        inout >> skey;
        for (int i = 0; i < key.size(); ++i) {
            if (key[i] == skey) {
                flag = 1
 
;
            }
        }
        if (flag == 1) {
            map[skey]++;
        } else {
            key.push_back(skey);
            map[skey] = 1;
        }
    }
    inout.close();
    vector<PAIR> pair_vec; //用pair來實現按照pair的第二個元素大小也就是value排序
    for (auto it = map.begin(); it != map.end(); it++) {
        pair_vec.push_back(make_pair(it->first, it->second));
    }
    stable_sort(pair_vec.begin(), pair_vec.end(), cmp);
    for (auto curr = pair_vec.begin(); curr != pair_vec.end(); ++curr) {
        cout << curr->first << " " << curr->second << endl;
    }
    return 0;
}

測試用例：

Everybody knows the famous and handsome football player David Beckham, who has a happy family. For a long time, this man’s wife was known to people as David’s beautiful wife, while the fact is that Victoria works so hard for her fashion circle and she makes it. Now everyone treats her as the fashion designer.

結果：