N queen problem code added

Author: me-shaon

Backtracking/N-Queen Problem/n-queen.c

@@ -0,0 +1,113 @@
+#include<stdio.h>
+#define EMPTY '-'
+#define QUEEN 'Q'
+
+char queen[100][100];
+int n;
+
+void initializeBoard(int n)
+{
+    int i,j;
+
+    for(i=1;i<=n;i++)
+    {
+        for(j=1;j<=n;j++)
+        {
+            queen[i][j] = EMPTY;
+        }
+    }
+}
+
+void printBoard()
+{
+    int i,j;
+
+    for(i=1;i<=n;i++)
+    {
+        for(j=1;j<=n;j++)
+        {
+            printf("%c ", queen[i][j]);
+        }
+        printf("\n");
+    }
+}
+
+int haveConflict(int row, int col)
+{
+    int i,j;
+
+    //check queen column
+    for(i=1;i<=n;i++)
+    {
+        if(queen[row][i] == QUEEN)
+            return 1;
+    }
+
+    //check queen row
+    for(i=1;i<row;i++)
+    {
+        if(queen[i][col] == QUEEN)
+            return 1;
+    }
+
+    //check upper left diagonal
+    for(i=row-1,j=col-1;i>0 && j>0;i--,j--)
+    {
+        if(queen[i][j] == QUEEN)
+            return 1;
+    }
+
+    //check upper right diagonal
+    for(i=row-1,j=col+1;i>0 && j<=n;i--,j++)
+    {
+        if(queen[i][j] == QUEEN)
+            return 1;
+    }
+
+    return 0;
+}
+
+//target is to place one queen in each row so that no one collides with each other
+//Here placed_queen parameter shows how much queen we've already placed, also how much row we've already covvered
+void backtrack(int placed_queen)
+{
+    int i, success = 0,next_move;
+    if(placed_queen > n) return; // All queens are placed properly
+
+    for(i=1;i<=n;i++)
+    {
+        if(queen[placed_queen][i] == QUEEN) //If we found already placed queen, remove it
+        {
+            //remove queen
+            queen[placed_queen][i] = EMPTY;
+            continue;
+        }
+
+        if(!haveConflict(placed_queen, i))
+        {
+            //place a queen piece
+            success = 1;
+
+            queen[placed_queen][i] = QUEEN;
+
+            break;
+        }
+    }
+
+    next_move = success ? (placed_queen + 1) : (placed_queen -1);
+
+    backtrack(next_move);
+}
+
+int main()
+{
+    scanf("%d", &n);
+
+    initializeBoard(n);
+
+    backtrack(0);
+
+    printBoard();
+
+    return 0;
+}