Create sudokusolver.c

Sudoju Solver using Recursion

misc/sudokusolver.c

@@ -0,0 +1,77 @@
+//recursion problem : Sudoku Solver
+/*You are given an incomplete N*N Sudoku and asked to solve it using the following recursive algorithm:
+(1) Scan the Sudoku from left to right row-wise to search for an empty cell.
+(2) If there are no empty cells, print the Sudoku. Go to step 5.
+(3) In the empty cell, try putting numbers 1 to N while ensuring that no two numbers in a single row, column, or box are same. Go back to step 1.
+(4) Declare that the Sudoku is Invalid.
+(5) Exit.*/
+
+#include <stdio.h>
+
+const int M=144;
+int N, R, C;
+
+int OKrow(int a[M], int x, int y, int v) {
+	int j;
+	for(j=0; j<N; j++)
+		if(a[x*N+j] == v)
+			return 0;
+	return 1;
+}
+int OKcol(int a[M], int x, int y, int v) {
+	int i;
+	for(i=0; i<N; i++)
+		if(a[i*N+y] == v)
+			return 0;
+	return 1;
+}
+int OKbox(int a[M], int x, int y, int v) {
+	int bi=x/R, bj=y/C, i, j;
+	for(i=0; i<R; i++)
+		for(j=0; j<C; j++)
+			if(a[(i + bi*R)*N + (j + bj*C)] == v)
+				return 0;
+	return 1;
+}
+int OK(int a[M], int x, int y, int v) {
+	return OKrow(a,x,y,v) && OKcol(a,x,y,v) && OKbox(a,x,y,v);
+}
+
+void print(int a[M]) {
+	int i, j;
+	for(i=0; i<N; i++)
+		for(j=0; j<N; j++)
+			printf("%d%c", a[i*N+j], (j==N-1 ? '\n':' '));
+}
+
+int solve(int a[M]) {
+	int i, j, v, rem=0;
+	for(i=0; i<N; i++) {
+		for(j=0; j<N; j++) {
+			if(a[i*N+j] == 0) {
+				rem = 1;
+				for(v=1; v<=N; v++) {
+					if(OK(a,i,j,v)) {
+						a[i*N+j] = v;
+						if(solve(a)) return 1;
+						a[i*N+j] = 0;
+					}
+				}
+			}
+		}
+	}
+	if(rem == 0) return 1;
+	return 0;
+}
+
+int main() {
+	scanf("%d%d%d", &N, &R, &C);
+	int a[M], i, j;
+	for(i=0; i<N; i++)
+		for(j=0; j<N; j++)
+			scanf("%d", &a[i*N+j]);
+
+	if(solve(a)) print(a);
+	else printf("Invalid\n");
+	return 0;
+}