HDOJ 3342 Legal or Not 【拓撲排序】

標籤：拓撲排序

題意：判斷是否成環。

策略：如題。

這道題就是簡單的拓撲排序題，但是要注意一點要去重複的資料。我用了兩種結構體：鏈式前向星和鄰接矩陣。

代碼1：（用鏈式前向星）（不用增加去重）

#include<stdio.h>#include<string.h>#include<queue>#define INF 0x3f3f3f3f#define MAXN 105struct EdgeNode{int to;int next;}edges[MAXN];int head[MAXN], n, in[MAXN], queue[MAXN];int toposort(){int i, iq = 0, j;for(i = 0; i < n; i ++){if(!in[i]){queue[iq++] = i;}}for(i = 0; i < iq; i ++){int temp = queue[i];for(j = head[temp]; j != -1; j = edges[j].next){if(!--in[edges[j].to]){queue[iq++] = edges[j].to;}}}return iq == n;}int main(){int m, a, b, i;while(scanf("%d%d", &n, &m), n||m){memset(head, -1, sizeof(head));memset(in, 0, sizeof(in));for(i = 0; i < m; i ++){scanf("%d%d", &a, &b);edges[i].to = b;edges[i].next = head[a];head[a] = i;++in[b];}printf("%s\n", toposort()?"YES":"NO");}}

代碼2：（用鄰接矩陣）事實證明鏈式前向星更快

#include<stdio.h>#include<string.h>#include<queue>#define INF 0x3f3f3f3f#define MAXN 105int map[105][105];int queue[MAXN], in[MAXN];int n;int toposort(){int i, j;int iq = 0;for(i = 0; i < n; i ++){if(!in[i]){queue[iq++] = i;}}for(i = 0; i < iq; i ++){int temp = queue[i];for(j = 0; j < n; j ++){if(map[temp][j]){--in[j];if(!in[j]){queue[iq++] = j;}}}}return iq == n;}int main(){int m, i, j, a, b;while(scanf("%d%d", &n, &m), n||m){memset(map, 0, sizeof(map));memset(in, 0, sizeof(in));for(i = 0; i < m; i ++){scanf("%d%d", &a, &b);if(!map[a][b]){ //去重map[a][b] = 1;in[b]++;}}printf("%s\n", toposort()?"YES":"NO");}return 0;} 

題目連結：http://acm.hdu.edu.cn/showproblem.php?pid=3342