N-queen_problem

algorithms/Bfs.c

@@ -0,0 +1,39 @@
+#include<stdio.h>
+int a[20][20], q[20], visited[20], n, i, j, f = 0, r = -1;
+void bfs(int v) {
+for(i = 1; i <= n; i++)
+if(a[v][i] && !visited[i])
+q[++r] = i;
+if(f <= r) {
+visited[q[f]] = 1;
+bfs(q[f++]);
+}
+}
+int main() {
+int v;
+printf("\n Enter the number of vertices:");
+scanf("%d", &n);
+for(i=1; i <= n; i++) {
+q[i] = 0;
+visited[i] = 0;
+}
+printf("\n Enter graph data in matrix form:\n");
+for(i=1; i<=n; i++) {
+for(j=1;j<=n;j++) {
+scanf("%d", &a[i][j]);
+}
+}
+printf("\n Enter the starting vertex:");
+
+scanf("%d", &v);
+bfs(v);
+printf("\n The node which are reachable are:\n");
+for(i=1; i <= n; i++) {
+if(visited[i])
+printf("%d\t", i);
+else {
+printf("\n Bfs is not possible. Not all nodes are reachable");
+break;
+}
+}
+}

algorithms/Dfs.c

@@ -0,0 +1,41 @@
+#include<stdio.h>
+int a[20][20],reach[20],n;
+void dfs(int v)
+{
+int i;
+reach[v]=1;
+
+for(i=1;i<=n;i++)
+if(a[v][i] && !reach[i])
+{
+printf("n %d->%d",v,i);
+dfs(i);
+}
+}
+int main()
+{
+int i,j,count=0;
+printf("\n Enter number of vertices:");
+scanf("%d",&n);
+for(i=1;i<=n;i++)
+{
+reach[i]=0;
+for(j=1;j<=n;j++)
+a[i][j]=0;
+}
+printf("\n Enter the adjacency matrix:\n");
+for(i=1;i<=n;i++)
+for(j=1;j<=n;j++)
+scanf("%d",&a[i][j]);
+dfs(1);
+printf("n");
+for(i=1;i<=n;i++)
+{
+if(reach[i])
+count++;
+}
+if(count==n)
+printf("\n Graph is connected");
+else
+printf("\n Graph is not connected");
+}

algorithms/divide-and-conquer/N-queen_problem.c

@@ -0,0 +1,61 @@
+#include<stdio.h>
+#include<math.h>
+int board[20],count;
+int main()
+{
+int n,i,j;
+void queen(int row,int n);
+
+printf("\n\nEnter number of Queens:");
+scanf("%d",&n);
+queen(1,n);
+return 0;
+}
+
+void print(int n)
+{
+int i,j;
+printf("\n\nSolution %d:\n\n",++count);
+for(i=1;i<=n;++i)
+printf("\t%d",i);
+for(i=1;i<=n;++i)
+{
+printf("\n\n%d",i);
+for(j=1;j<=n;++j)
+{
+if(board[i]==j)
+printf("\tQ");
+else
+printf("\t-");
+}
+}
+}
+int place(int row,int column)
+{
+int i;
+
+for(i=1;i<=row-1;++i)
+{
+if(board[i]==column)
+return 0;
+else
+if(abs(board[i]-column)==abs(i-row))
+return 0;
+}
+return 1;
+}
+void queen(int row,int n)
+{
+int column;
+for(column=1;column<=n;++column)
+{
+if(place(row,column))
+{
+board[row]=column;
+if(row==n)
+print(n);
+else
+queen(row+1,n);
+}
+}
+}

stringpatternsearching.c

@@ -0,0 +1,54 @@
+#include <stdio.h>
+#include <string.h>
+int match(char [], char []);
+
+int main() {
+  char a[100], b[100];
+  int position;
+
+  printf("Enter some text\n");
+  scanf("%s",&a);
+
+  printf("Enter a string to find\n");
+  scanf("%s",&b);
+
+  position = match(a, b);
+
+  if (position != -1) {
+    printf("Found at location: %d\n", position + 1);
+  }
+  else {
+    printf("Not found.\n");
+  }
+
+  return 0;
+}
+
+int match(char text[], char pattern[]) {
+  int c, d, e, text_length, pattern_length, position = -1;
+
+  text_length    = strlen(text);
+  pattern_length = strlen(pattern);
+
+  if (pattern_length > text_length) {
+    return -1;
+  }
+
+  for (c = 0; c <= text_length - pattern_length; c++) {
+    position = e = c;
+
+    for (d = 0; d < pattern_length; d++) {
+      if (pattern[d] == text[e]) {
+        e++;
+      }
+      else {
+        break;
+      }
+    }
+    if (d == pattern_length) {
+      return position;
+    }
+  }
+
+  return -1;
+}