Islands

Islands

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这是道水题，每一个联通块是一个小岛，求问小岛边长与面积比的最大值和最小值。
直接在图上dfs就好了，记录每个小岛面积以及周长（即dfs下一步会到达水域位置）。
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#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <string>

const int maxn = 500;
char map[maxn][maxn];
struct Node {
    int area, l;
}f[maxn*maxn];
int a[maxn][maxn];
bool flag[maxn][maxn];
int n, t;

const int dir[4][2] = {{0, 1}, {1, 0}, {0, -1}, {-1, 0}};

void island_dfs(int x, int y, int num) {
    int x1, y1;
    a[x][y] = num;
    flag[x][y] = true;
    f[num].area++;
    for (int k = 0; k < 4; k++) {
        x1 = x+dir[k][0];
        y1 = y+dir[k][1];
        if (x1 < 0 || x1 > n+1 || y1 < 0 || y1 > n+1) continue;
        if (map[x1][y1] == '.') {
            f[num].l++;
            continue;
        }
        if (flag[x1][y1] || map[x1][y1] != 'X') continue;
        island_dfs(x1, y1, num);
    }
}
int main() {
    char c;
    while (scanf("%d", &n) != EOF) {
        if (n == 0) break;
        memset(f, 0, sizeof(f));
        for (int i = 1; i <= n; i++) {
            scanf("%c", &c);
            for (int j = 1; j <= n; j++)
                scanf("%c", &map[i][j]);
        }
        for (int i = 0; i <= n+1; i++) {
            map[i][0] = '.';
            map[0][i] = '.';
            map[n+1][i] = '.';
            map[i][n+1] = '.';
        }
        memset(a, 0, sizeof(a));
        memset(flag, 0, sizeof(flag));
        t = 0;
        for (int i = 1; i <= n; i++)
            for (int j = 1; j <= n; j++) if (!flag[i][j] && map[i][j] == 'X') {
                t++;
                island_dfs(i, j, t);
            }
        double maxx = 0, minn = 1000000;
        for (int i = 1; i <= t; i++) {
            double t1 = f[i].area;
            double t2 = f[i].l;
            if (t2/t1 > maxx) maxx = t2/t1;
            if (t2/t1 < minn) minn = t2/t1;
        }
        printf("%.6lf %.6lf\n", maxx, minn);

    }   
}