[convex hall] ZOJ 1518 This Sentence is False

最新推荐文章于 2022-11-17 00:47:51 发布

原创最新推荐文章于 2022-11-17 00:47:51 发布 · 523 阅读

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#graph

本文介绍了一种用于判断一组特定格式句子之间是否一致的算法。通过构建图模型，并使用深度优先搜索（DFS）进行图着色来解决该问题。若句子间存在矛盾，则输出“Inconsistent”，否则输出真值句子的最大数量。

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题目是说有n个句子(编号为1-n)，每句格式为Sentence x is true(false).
然后判断这些句子是否是一致的，如果不一致，输出Inconsistent
否则输出为句子为真的最大个数

做法(参考呆滞的慢板的提示)是若第x句为Sentence y is true则x，y之间连同色边
否则连异色边
n句都读完后，对顶点dfs着色，如果xy之间连同色边，则x，y着同色，否则异色
如果着色发生冲突，则输出Inconsistent
否则对于一个连通分量取顶点个数多的那一个加到res中

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int NOT_COLORED = -1;
const int NOT_CONNECT = -1;
const int SAME = 0;
const int DIFF = 1;
const int MAXN = 1001;
int graph[MAXN][MAXN];
int vertex[MAXN];
int sum[2];
bool visit[MAXN];
bool consistent;
char buff[80];
void dfs(const int x, const int n) {
    int i, j, k;
    if (!consistent) return;
    for (i=1; i<=n; ++i) {
        if (!visit[i]) {
            if (graph[x][i] == SAME) {
                visit[i] = true;
                if (vertex[i] == NOT_COLORED) {
                    vertex[i] = vertex[x];
                    ++sum[vertex[i]];
                    dfs(i, n);
                } else if (vertex[x]^vertex[i]) {
                    consistent = false;
                    return;
                }
            } else if (graph[x][i] == DIFF) {
                visit[i] = true;
                if (vertex[i] == NOT_COLORED) {
                    vertex[i] = vertex[x] ^ 1;
                    ++sum[vertex[i]];
                    dfs(i, n);
                } else if (vertex[x] == vertex[i]) {
                    consistent = false;
                    return;
                }
            }
        } else {
            if (graph[x][i] == SAME && (vertex[x] ^ vertex[i])) {
                consistent = false;
                return;
            }
            if (graph[x][i] == DIFF && vertex[x] == vertex[i]) {
                consistent = false;
                return;
            }
        }
    }
}
void gao(const int n) {
    int i, j, k;
    int res(0);
    memset(visit, false, sizeof(visit));
    memset(vertex, NOT_COLORED, sizeof(vertex));
    for (i=1; i<=n; ++i) {
        if (!visit[i]) {
            visit[i] = true;
            consistent = true;
            vertex[i] = 0;
            sum[0] = 1, sum[1] = 0;
            dfs(i, n);
            if (!consistent) break;
            res += max(sum[0], sum[1]);
        }
    }
    if (!consistent) puts("Inconsistent");
    else printf("%d/n", res);
}
int main() {
    int x, y, n;
    int i, j, k;
    //freopen("f://in.txt", "r", stdin);
    //freopen("f://out.txt", "w", stdout);
    scanf("%d", &n);
    while (n != 0) {
        consistent = true;
        memset(graph, NOT_CONNECT, sizeof(graph));
        for (i=1; i<=n; ++i) graph[i][i] = SAME;
        for (x=1; x<=n; ++x) {
            scanf("%s %d %s %s", buff, &y, buff, buff);
            if (consistent) {
                if (buff[0] == 't') {
                    if (graph[x][y] == DIFF) {
                        consistent = false;
                        continue;
                    }
                    graph[x][y] = graph[y][x] = SAME;
                } else {
                    if (graph[x][y] == SAME) {
                        consistent = false;
                        continue;
                    }
                    graph[x][y] = graph[y][x] = DIFF;
                }
            }
        }
        if (!consistent) puts("Inconsistent");
        else gao(n);
        scanf("%d", &n);
    }
    return 0;
}