【HDOJ】4932 Miaomiao's Geometry

递归检测。因为dis数组开的不够大，各种wa。写了个数据发生器，果断发现错误，改完就过了。

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>

using namespace std;

#define MAXN 55

int n;
double a[MAXN], dis[MAXN*2];
char visit[MAXN]; // 0: false, 1: left, 2:right

bool dfs(int x, double l) {
    if (x == n-1)
        return true;
    if (x == 0) {
        visit[x] = 2;
        return dfs(x+1, l);
    }
    if (visit[x-1] == 2) {
        if (a[x-1]+l <= a[x]) {
            visit[x] = 2;
            if ( dfs(x+1, l) )
                return true;
        } else if (a[x]+l <= a[x+1]) {
            visit[x] = 1;
            return dfs(x+1, l);
        }
        return false;
    } else {
        if (a[x-1]+2*l <= a[x] || a[x-1]+l==a[x]) {
            visit[x] = 2;
            if ( dfs(x+1, l) )
                return true;
        } else if (a[x]+l <= a[x+1]) {
            visit[x] = 1;
            return dfs(x+1, l);
        }
        return false;
    }
}

int main() {
    //FILE *fout = fopen("data", "w");
    int case_n, m;
    int i;

    scanf("%d", &case_n);
    while (case_n--) {
        scanf("%d", &n);
        for (i=0; i<n; ++i)
            scanf("%lf", &a[i]);
        sort(a, a+n);
        for (m=0, i=1; i<n; ++i) {
            dis[m++] = a[i] - a[i-1];
            dis[m++] = (a[i] - a[i-1])/2;
        }
        sort(dis, dis+m);
        dis[m] = 0.0f;
        for (i=m-1; i>=0; --i) {
            if (dis[i] != dis[i+1]) {
                memset(visit, 0, sizeof(visit));
                if ( dfs(0, dis[i]) )
                    break;
            }
        }
        printf("%.3lf
", dis[i]);
        //fprintf(fout, "%.3lf
", dis[i]);
    }

    return 0;
}