Changes

//Used to remember which row | col | box for ( section int i = 0; i < N; ++i) have which values __shared__ bool notSeen[i] = true; rowHas[Ncol][Nrow]= false; __shared__ bool colHas[Ncol][Nrow]= false; __shared__ bool boxHas[Ncol][Nrow]= false; __syncthreads();

//Used to ensure that the table has changed if (at != UNASSIGNED) { __shared__ bool changed rowHas[row][at - 1] = true; colHas[col][at - 1] = true; boxHas[box][at - 1] = true; }

//Number of spaces which can place the number in each sectionPrevious loop has not changed any values __shared__ int do { //RESET counters rowCount[Ncol][Nrow]= 0; __shared__ int colCount[Ncol][Nrow]= 0; __shared__ int boxCount[Ncol][Nrow]= 0; __syncthreads(); if (gridIdx == 0) //forget previous change changed = false;

int count = 0; //number of values which can fit in this square int guess = 0; //last value found which can fit in this square for (int idx = 0; idx < N; ++idx) { //Where the Ensures that every square in each section is located working on a different number in the Sudokusection int row num = threadIdx.x(idx + offset) % N; int if (at == UNASSIGNED && notSeen[num]){ if (rowHas[row][num] || boxHas[box][num] || colHas[col ][num]){ notSeen[num] = threadIdx.yfalse; } else { ++count; int box guess = num; rowCount[row ][num] ++; colCount[col][num] ++; boxCount[box][num] ++; } } __syncthreads(); } / BOXWIDTH /Find values which can go in only one spot in the section for (int idx = 0; idx < N && count > 1; + +idx) { if (notSeen[idx] && (rowCount[row][idx] == 1 || boxCount[box][idx] == 1 || colCount[col ][idx] == 1)) { / BOXWIDTH/In this section this value can only appear in this square guess = idx; count = 1; } } if (count == 1) { at = guess + 1; rowHas[row][guess] = true; colHas[col][guess] = true; boxHas[box][guess] = true; changed = true; } __syncthreads(); } while (changed ) * BOXWIDTH;

//Unique identifier for each square in row, col, box //Corresponds to the generic Sudoku Solve //Using a Sudoku to solve a Sudoku !!! int offset = col + (row % BOXWIDTH) * BOXWIDTH + (box % BOXWIDTH);  //Square's location in the Sudoku int gridIdx = col * N + row;  int at = d_a[gridIdx];  bool notSeen[N];  for (int i = 0; i < N; ++i) notSeen[i] = true;  rowHas[col][row] = false; colHas[col][row] = false; boxHas[col][row] = false; __syncthreads();  if (at != UNASSIGNED) { rowHas[row][at - 1] = true; colHas[col][at - 1] = true; boxHas[box][at - 1] = true; }  //Previous loop has not changed any values do { //RESET counters rowCount[col][row] = 0; colCount[col][row] = 0; boxCount[col][row] = 0; __syncthreads();  if (gridIdx == 0) //forget previous change changed = false; int count = 0; //number of values which can fit in this square int guess = 0; //last value found which can fit in this square for (int idx = 0; idx < N; ++idx) { //Ensures that every square in each section is working on a different number in the section int num = (idx + offset) % N; if (at == UNASSIGNED && notSeen[num]){ if (rowHas[row][num] || boxHas[box][num] || colHas[col][num]){ notSeen[num] = false; } else { ++count; guess = num; rowCount[row][num] ++; colCount[col][num] ++; boxCount[box][num] ++; } } __syncthreads(); }  //Find values which can go in only one spot in the section for (int idx = 0; idx < N && count > 1; ++idx) { if (notSeen[idx] && ( rowCount[row][idx] == 1 || boxCount[box][idx] == 1 || colCount[col][idx] == 1)) { //In this section this value can only appear in this square guess = idx; count = 1; } } if (count == 1) { at = guess + 1; rowHas[row][guess] = true; colHas[col][guess] = true; boxHas[box][guess] = true; changed = true; } __syncthreads(); } while (changed );  d_a[gridIdx] = at;}