How to solve another version of Kakuro - c++

Question

The problem is, in a table of (h+1)*(w+1),the first row contains w values: a[1] ... a[w] which fill in the 2rd ... (w+1)th column. The first column contains h values: b[1] ... b[h] which fill in the 2rd ... (h+1)th row. sum(a[i]) is equal to sum(b[i]).
The question is to give one possible solution: result, so that sum(result[i][K]) for a certain K, is equal to a[i] with result[i][K] != result[j][K] (i != j and 0 < i < h+1). And the same rule for rows. PS: All the integers are positive.
For example:
a[] = {10, 3, 3}, b[] = {9, 7}
// 10 3 3
// 9 6 2 1
// 7 4 1 2
result = {6, 2, 1;
4, 1, 2}
It is like Kakuro but not the same. I cannot figure out which algorithm to apply, if anyone knows how to solve it, please give me some help. Thanks a lot.

Answer 1

You can always solve your problem with backtracking. Basic idea here: from top-to-bottom and left-to-right try a valid value in the partially filled table, backtrack when this value doesn't lead to a solution.
Minimal example in C++ with annotated solve:
#include <algorithm>
#include <iostream>
#include <iterator>
#include <memory>
class Problem {
public:
template<class AIter, class BIter>
Problem(AIter abegin, AIter aend, BIter bbegin, BIter bend)
: m_width(std::distance(abegin, aend))
, m_height(std::distance(bbegin, bend))
, m_table(new int[(m_width + 1) * (m_height + 1)])
{
std::fill(m_table.get(), m_table.get() + (m_width + 1) * (m_height + 1), 0);
for(size_t i = 0; i < m_width; ++i)
m_table[i + 1] = *abegin++;
for(size_t j = 0; j < m_height; ++j)
m_table[(j + 1) * (m_width + 1)] = *bbegin++;
}
bool Solve() { return solve(0, 0); }
int operator()(size_t i, size_t j) const;
private:
int a(size_t i) const { return m_table[i + 1]; }
int b(size_t j) const { return m_table[(j + 1) * (m_width + 1)]; }
int get(size_t i, size_t j) const { return m_table[(j + 1) * (m_width + 1) + i + 1]; }
void set(size_t i, size_t j, int value) { m_table[(j + 1) * (m_width + 1) + i + 1] = value; }
int colSum(size_t i) const;
int rowSum(size_t j) const;
bool solve(size_t i, size_t j);
size_t m_width, m_height;
std::unique_ptr<int[]> m_table; // (width + 1) x (height + 1)
};
int Problem::colSum(size_t i) const {
int sum = 0;
for(size_t j = 0; j < m_height; ++j)
sum += get(i, j);
return sum;
}
int Problem::rowSum(size_t j) const {
int sum = 0;
for(size_t i = 0; i < m_width; ++i)
sum += get(i, j);
return sum;
}
// solves column-wise using backtracking
bool Problem::solve(size_t i, size_t j) {
size_t width = m_width, height = m_height;
// past last column?
if(i >= width) {
// found solution
return true;
}
// remainder in column and row
int remColSum = a(i) - colSum(i);
int remRowSum = b(j) - rowSum(j);
// early break
if(remColSum <= 0 || remRowSum <= 0)
return false;
// starting at the minimal required value (1 or remColSum if on last row)
int startValue = j + 1 < height ? 1 : remColSum;
// remaining row sum cannot support the starting value
if(remRowSum < startValue)
return false;
// end value minimum remaining sum
int endValue = remColSum < remRowSum ? remColSum : remRowSum;
// on last element must equal starting value
if(i + 1 == width && j + 1 == height && startValue != endValue)
return false;
// column-wise i.e. next cell is (i, j + 1) wrapped
int nextI = i + (j + 1) / height;
int nextJ = (j + 1) % height;
for(int value = startValue; value <= endValue; ++value) {
bool valid = true;
// check row up to i
for(size_t u = 0; u < i && valid; ++u)
valid = (get(u, j) != value);
// check column up to j
for(size_t v = 0; v < j && valid; ++v)
valid = (get(i, v) != value);
if(!valid) {
// value is invalid in partially filled table
continue;
}
// value produces a valid, partially filled table, now try recursing
set(i, j, value);
// upon first solution break
if(solve(nextI, nextJ))
return true;
}
// upon failure backtrack
set(i, j, 0);
return false;
}
int Problem::operator()(size_t i, size_t j) const {
return get(i, j);
}
int main() {
int a[] = { 10, 3, 3 };
int b[] = { 9, 7 };
size_t width = sizeof(a) / sizeof(*a);
size_t height = sizeof(b) / sizeof(*b);
Problem problem(a, a + width, b, b + height);
if(!problem.Solve()) {
std::cout << "No solution" << std::endl;
}
for(size_t j = 0; j < height; ++j) {
if(j == 0) {
std::cout << " ";
for(size_t i = 0; i < width; ++i)
std::cout << " " << a[i];
std::cout << std::endl;
}
std::cout << b[j];
for(size_t i = 0; i < width; ++i) {
int value = problem(i, j);
if(value == 0)
std::cout << " ";
else
std::cout << " " << value;
}
std::cout << std::endl;
}
return 0;
}