回答編集履歴
1
追記
answer
CHANGED
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@@ -13,4 +13,116 @@
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13
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cities[2]～cities[市の数-1] の中から 八王子市（35.67，139.32）に最も近い
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cities[x]を見つけ、cities[2]と交換する
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-
これだけやれば、距離が近い市3位までを cities[0],cities[1],cities[2] に求めたことになります。
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これだけやれば、距離が近い市3位までを cities[0],cities[1],cities[2] に求めたことになります。
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[追記] 15分で書いたやつ：
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```C
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#define _CRT_SECURE_NO_WARNINGS /* disable warning only for VC++ */
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#include <stdio.h>
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#include <stdio.h>
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#include <stdlib.h>
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#include <math.h>
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#include <string.h>
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typedef struct {
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char name[32];
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double lat;
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double lng;
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} City;
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32
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// ファイル:path を読み、City列を *pcities に求める
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// 都市の数を返す
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int build_cities(const char* path, City** pcities) {
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int n;
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City* c;
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FILE* fp = fopen(path,"r");
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if ( fp == NULL ) return 0;
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fscanf(fp, "%d", &n);
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c = (City*)malloc(sizeof(City)*n);
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if ( c != NULL ) {
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int i;
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*pcities = c;
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for ( i = 0; i < n; ++i ) {
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fscanf(fp, "%s %lf %lf", c[i].name, &c[i].lat, &c[i].lng);
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}
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}
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fclose(fp);
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return n;
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}
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void print_city(const City* city) {
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printf("%s %lf %lf\n", city->name, city->lat, city->lng);
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}
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void print_cities(const City* cities, int ncities) {
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int i;
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for (i = 0; i < ncities; ++i) {
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print_city(&cities[i]);
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}
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}
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// cities[begin]～cities[ncities-1] の中からtargetに最も近い cities[n] を求め n を返す。
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// 2都市間の距離は fdistance により算出する
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int nearest_city(const City* cities, int ncities, int begin,
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const City* target, double (*fdistance)(const City*, const City*) ) {
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int i;
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int nearest = 0;
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double nearest_distance = 0.0;
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for ( i = begin; i < ncities; ++i ) {
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double distance = fdistance(&cities[i], target);
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if ( i == begin || nearest_distance > distance ) {
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nearest = i;
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nearest_distance = distance;
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}
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}
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return nearest;
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}
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// 都市 a と b を交換する
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void swap_city(City* a, City* b) {
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City tmp = *a;
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*a = *b;
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*b = tmp;
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}
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// (なんちゃって)マンハッタン距離
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double manhattan_distance(const City* a, const City* b) {
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return fabs(a->lng - b->lng) + fabs(a->lng - b->lng);
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}
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int main(int argc, char* argv[]) {
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City target;
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City* cities;
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int ncities;
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int n;
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/*
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const char* path = argv[1];
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strcpy(target.name, argv[2]);
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target.lat = atof(argv[3]);
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target.lng = atof(argv[4]);
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*/
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const char* path = "data/coord.dat";
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strcpy(target.name, "八王子市");
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target.lat = 35.66657;
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target.lng = 139.3161;
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108
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ncities = build_cities(path, &cities);
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//print_cities(cities, ncities);
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// nearest 3
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n = nearest_city(cities, ncities, 0, &target, manhattan_distance);
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swap_city(&cities[0], &cities[n]);
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n = nearest_city(cities, ncities, 1, &target, manhattan_distance);
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swap_city(&cities[1], &cities[n]);
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n = nearest_city(cities, ncities, 2, &target, manhattan_distance);
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swap_city(&cities[2], &cities[n]);
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printf("nearest 3 cities from: ");
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print_city(&target);
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puts("---------------");
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print_cities(cities, 3);
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free(cities);
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return 0;
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}
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128
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```
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