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find-valid-matrix-given-row-and-column-sums.cpp
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find-valid-matrix-given-row-and-column-sums.cpp
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// Time: O(m + n), excluding ctor of result
// Space: O(1)
// optimized from Solution2 since we can find next i, j pair without nested loops
class Solution {
public:
vector<vector<int>> restoreMatrix(vector<int>& rowSum, vector<int>& colSum) {
vector<vector<int>> matrix(size(rowSum), vector<int>(size(colSum)));
for (int i = 0, j = 0; i < size(matrix) && j < size(matrix[0]);) {
matrix[i][j] = min(rowSum[i], colSum[j]); // greedily used
rowSum[i] -= matrix[i][j];
colSum[j] -= matrix[i][j];
if (!rowSum[i]) { // won't be used in row i, ++i
++i;
}
if (!colSum[j]) { // won't be used in col j, ++j
++j;
}
}
return matrix;
}
};
// Time: O(m * n)
// Space: O(1)
class Solution2 {
public:
vector<vector<int>> restoreMatrix(vector<int>& rowSum, vector<int>& colSum) {
vector<vector<int>> matrix(size(rowSum), vector<int>(size(colSum)));
for (int i = 0; i < size(matrix); ++i) {
for (int j = 0 ;j < size(matrix[0]); ++j) {
matrix[i][j] = min(rowSum[i], colSum[j]); // greedily used
rowSum[i] -= matrix[i][j];
colSum[j] -= matrix[i][j];
}
}
return matrix;
}
};