mirror of https://github.com/TheAlgorithms/C
78 lines
1.6 KiB
C
78 lines
1.6 KiB
C
//recursion problem : Sudoku Solver
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/*You are given an incomplete N*N Sudoku and asked to solve it using the following recursive algorithm:
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(1) Scan the Sudoku from left to right row-wise to search for an empty cell.
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(2) If there are no empty cells, print the Sudoku. Go to step 5.
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(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.
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(4) Declare that the Sudoku is Invalid.
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(5) Exit.*/
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#include <stdio.h>
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const int M=144;
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int N, R, C;
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int OKrow(int a[M], int x, int y, int v) {
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int j;
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for(j=0; j<N; j++)
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if(a[x*N+j] == v)
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return 0;
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return 1;
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}
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int OKcol(int a[M], int x, int y, int v) {
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int i;
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for(i=0; i<N; i++)
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if(a[i*N+y] == v)
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return 0;
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return 1;
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}
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int OKbox(int a[M], int x, int y, int v) {
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int bi=x/R, bj=y/C, i, j;
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for(i=0; i<R; i++)
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for(j=0; j<C; j++)
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if(a[(i + bi*R)*N + (j + bj*C)] == v)
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return 0;
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return 1;
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}
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int OK(int a[M], int x, int y, int v) {
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return OKrow(a,x,y,v) && OKcol(a,x,y,v) && OKbox(a,x,y,v);
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}
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void print(int a[M]) {
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int i, j;
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for(i=0; i<N; i++)
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for(j=0; j<N; j++)
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printf("%d%c", a[i*N+j], (j==N-1 ? '\n':' '));
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}
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int solve(int a[M]) {
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int i, j, v, rem=0;
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for(i=0; i<N; i++) {
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for(j=0; j<N; j++) {
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if(a[i*N+j] == 0) {
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rem = 1;
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for(v=1; v<=N; v++) {
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if(OK(a,i,j,v)) {
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a[i*N+j] = v;
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if(solve(a)) return 1;
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a[i*N+j] = 0;
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}
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}
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}
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}
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}
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if(rem == 0) return 1;
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return 0;
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}
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int main() {
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scanf("%d%d%d", &N, &R, &C);
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int a[M], i, j;
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for(i=0; i<N; i++)
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for(j=0; j<N; j++)
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scanf("%d", &a[i*N+j]);
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if(solve(a)) print(a);
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else printf("Invalid\n");
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return 0;
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}
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