mirror of https://github.com/TheAlgorithms/C
94 lines
1.8 KiB
C
94 lines
1.8 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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#define 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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{
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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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{
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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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{
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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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{
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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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{
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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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{
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int i, j, v, rem = 0;
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for (i = 0; i < N; i++)
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{
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for (j = 0; j < N; j++)
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{
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if (a[i * N + j] == 0)
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{
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rem = 1;
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for (v = 1; v <= N; v++)
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{
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if (OK(a, i, j, v))
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{
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a[i * N + j] = v;
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if (solve(a))
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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)
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return 1;
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return 0;
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}
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int main()
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{
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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))
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print(a);
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else
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printf("Invalid\n");
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return 0;
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}
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