K-Means的简单实现

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <algorithm>
#include <utility>

using namespace std;

const int MAXN(100010);
const int MAXK(100010);
const int MAXC(5);

template<typename T>
inline bool checkmax(T &a, const T &b){
    return a > b? ((a = b), true): false;
}

template<typename T>
inline T ABS(T a){
    return a < 0? -a: a;
}

struct PO{  //点定义
    double co[MAXC];
} po[MAXN];
PO reg[MAXK];  //基准点
int qua[MAXK]; //每类包含点数
int bel[MAXN], ind[MAXN]; //点i属于bel[i]，初始选择基准点所需索引

double dis(const PO &a, const PO &b, int C){
    double ret = 0;
    for(int i = 0; i < C; ++i) ret += (a.co[i]-b.co[i])*(a.co[i]-b.co[i]);
    return ret;
}

void ini_reg(int n, int K){  //从n个点中随机选择K个点
    srand(2357);
    for(int i = 0; i < n; ++i) ind[i] = i;
    for(int i = 0; i < K; ++i){
        int j = ((double)rand()/RAND_MAX)*(n-i)+i;
        swap(ind[i], ind[j]);
    }
    for(int i = 0; i < K; ++i) reg[i] = po[ind[i]];
}

void cal_reg(int n, int K, int C){  //重新计算基准点
    for(int i = 0; i < K; ++i){
        qua[i] = 0;
        for(int j = 0; j < C; ++j)
            reg[i].co[j] = 0;
    }
    for(int i = 0; i < n; ++i){
        ++qua[bel[i]];
        for(int j = 0; j < C; ++j) reg[bel[i]].co[j] += po[i].co[j];
    }
    for(int i = 0; i < K; ++i)
        for(int j = 0; j < C; ++j)
            reg[i].co[j] /= qua[i];
}

void solve(int n, int K, int C, double err){  //K-means
    bool fir(true);
    double F_, F(0);
    do{
        if(fir){
            ini_reg(n, K);
            fir = false;
        }
        else
            cal_reg(n, K, C);
        F_ = F;
        F = 0;
        for(int j = 0; j < n; ++j){
            int id = 0;
            double md = dis(po[j], reg[0], C);
            for(int k = 1; k < K; ++k){
                double t = dis(po[j], reg[k], C);
                if(t < md){
                    md = t;
                    id = k;
                }
            }
            bel[j] = id;
            F += md;
        }
    } while(ABS(F_-F) > err);
}

int main(){
    int n, K, C;  //点数，类数，向量维数
    double err;  //阀值
    //input
    scanf("%d%d%d%lf", &n, &K, &C, &err);
    for(int i = 0; i < n; ++i)
        for(int j = 0; j < C; ++j)
            scanf("%lf", po[i].co+j);
    solve(n, K, C, err);
    printf("\n");
    for(int i = 0; i < n; ++i) printf(" %d", bel[i]);
    //end
    return 0;
}

/*
20 4 2 0.2
0.1 0.1
0.1 0.2
0.2 0.1
0.5 0.5
1 1
1.1 2.2
1.1 2.3
1.1 2.4
1.1 2.5
1.5 1.5
3.1 -1.3
3.1 -1.4
3.1 -1.5
3.1 -1.6
3.5 -1.7
4.1 3.5
4.1 3.6
4.1 3.7
4.1 3.8
4.1 5.0
*/