From 0282e6aa2f3b24a3ffed876b099ec97e6a79a8ff Mon Sep 17 00:00:00 2001
From: Teddy <ted.sybil@gmail.com>
Date: Fri, 25 Apr 2014 21:47:32 +0800
Subject: code snippets for dominant frontier

---
 dom.c | 155 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 155 insertions(+)
 create mode 100644 dom.c

diff --git a/dom.c b/dom.c
new file mode 100644
index 0000000..7fbd948
--- /dev/null
+++ b/dom.c
@@ -0,0 +1,155 @@
+#include <stdio.h>
+#include <string.h>
+#include <stdlib.h>
+#define MAXN 1000
+#define MAX_HASH 1021
+typedef struct Edge Edge;
+typedef struct Set Set;
+typedef Set *Set_t;
+typedef struct SetNode {
+        int val;
+        struct SetNode *next;        
+} SetNode;
+struct Set {
+    SetNode *head[MAX_HASH];
+};
+
+Set_t set_create() {
+    Set_t set = (Set_t)malloc(sizeof(Set));
+    memset(set->head, 0, sizeof set->head);
+    return set;
+}
+
+int set_belongs(Set_t set, int val) {
+    SetNode *p;
+    for (p = set->head[val % MAX_HASH]; p; p = p->next)
+        if (p->val == val) return 1;
+    return 0;
+}
+
+void set_push(Set_t set, int val) {
+    SetNode *p = (SetNode*)malloc(sizeof(SetNode));
+    int hv = val % MAX_HASH;
+    p->next = set->head[hv];
+    p->val = val;
+    set->head[hv] = p;
+}
+
+struct Edge {
+    int to;
+    Edge *next;
+} *head[MAXN], *rhead[MAXN];
+
+typedef struct DFNode DFNode;
+struct DFNode {
+    int id;
+    DFNode *next;
+};
+
+void add_edge(int a, int b, Edge **head) {
+    Edge *p = (Edge*)malloc(sizeof(Edge));
+    p->to = b;
+    p->next = head[a];
+    head[a] = p;
+}
+int dom[MAXN], ord[MAXN], vis[MAXN], par[MAXN];
+int n, n0, m;
+DFNode *df[MAXN];
+Set_t dfset[MAXN];
+
+void dfs(int u, int v) {
+    static int ocnt = 0;
+    Edge *e;
+    if (vis[u] != -1) return;
+    par[u] = v;
+    vis[u] = 0;
+    for (e = head[u]; e; e = e->next)
+        dfs(e->to, u);
+    vis[u] = ocnt;
+    ord[ocnt++] = u;
+}
+
+int intersect(int b1, int b2) {
+    while (b1 != b2)
+        if (b1 < b2) b1 = dom[b1];
+        else b2 = dom[b2];
+    return b1;
+}
+
+int main() {
+    int i;
+    int ch = 1; 
+    scanf("%d %d %d", &n, &m, &n0);
+    for (i = 0; i < m; i++)
+    {
+        int a, b;
+        scanf("%d %d", &a, &b);
+        add_edge(a, b, head);
+        add_edge(b, a, rhead);
+    }
+    for (i = 0; i < n; i++)
+        vis[i] = dom[i] = -1;
+    dfs(n0, -1);
+    for (i = 0; i < n; i++)
+        printf("%d ", ord[i]); puts("");
+    dom[vis[n0]] = vis[n0];
+    while (ch)
+    {
+        int i;
+        ch = 0;
+        for (i = n - 2; i >= 0; i--)
+        {
+            int id = ord[i];
+            Edge *e = rhead[id];
+            int new_idom = vis[par[id]];
+            for (; e; e = e->next)
+            {
+                int p = e->to;
+                if (p == new_idom) continue;
+                if (dom[vis[p]] != -1)
+                    new_idom = intersect(vis[p], new_idom);
+            }
+            if (dom[i] != new_idom)
+            {
+                ch = 1;
+                dom[i] = new_idom;
+            }
+        }
+        for (i = 0; i < n; i++)
+            printf("%d ", ord[dom[vis[i]]]); puts("");
+    }
+    for (i = 0; i < n; i++)
+    {
+        dfset[i] = set_create();
+        df[i] = NULL;
+    }
+    for (i = 0; i < n; i++)
+        if (rhead[i] && rhead[i]->next)
+        {
+            Edge *p = rhead[i];
+            for (; p; p = p->next)
+            {
+                int runner = p->to;
+                while (vis[runner] != dom[vis[i]])
+                {
+                    if (!set_belongs(dfset[runner], i))
+                    {
+                        DFNode *np = (DFNode*)malloc(sizeof(DFNode));
+                        np->id = i;
+                        np->next = df[runner];
+                        set_push(dfset[runner], i);
+                        df[runner] = np;
+                    }
+                    runner = ord[dom[vis[runner]]];
+                }
+            }
+        }
+    for (i = 0; i < n; i++)
+    {
+        DFNode *p = df[i];
+        printf("%d: ", i);
+        for (; p; p = p->next)
+            printf("%d ", p->id); puts("");
+    }
+    return 0;
+}
-- 
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