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-rw-r--r--find_good_subset_matrix.c89
1 files changed, 89 insertions, 0 deletions
diff --git a/find_good_subset_matrix.c b/find_good_subset_matrix.c
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+// 2732. Find a Good Subset of the Matrix
+#include "leetcode.h"
+
+/*
+ * you are given a 0-indexed 'm * n' binary matrix 'grid'. let us call a
+ * non-empty subset of rows good if the sum of each column of the subset is at
+ * most half of the length of the subset. more formally, if the length of the
+ * chosen subset of rows is 'k', then the sum of each column should be at most
+ * 'floor(k / 2)'. return an integer array that contains row indices of a good
+ * subset sorted in ascending order. if there are multiple answers, you can
+ * return any of them. if there are no good subsets, return an empty array. a
+ * subset of rows of the matrix 'grid' is any matrix that can be obtained by
+ * deleting some (possibly none) rows from 'grid'
+ */
+
+static uint encode(const int *row, int rowSize) {
+ uint x = 0;
+ for (int i = 0; i < rowSize; ++i) {
+ if (!row[i])
+ continue;
+ x |= 1 << i;
+ }
+ return x;
+}
+
+int *goodSubsetofBinaryMatrix(int **grid, int gridSize, int *gridColSize,
+ int *returnSize) {
+ const int n = 1 << *gridColSize;
+ int *idx = (int *)malloc(n * sizeof(int));
+ memset(idx, -1, n * sizeof(int));
+ for (int i = gridSize - 1; i >= 0; --i)
+ idx[encode(grid[i], gridSize)] = i;
+ if (idx[0] != -1) {
+ *returnSize = 1;
+ int *ans = (int *)malloc(*returnSize * sizeof(int));
+ ans[0] = idx[0];
+ free(idx);
+ return ans;
+ }
+ for (int a = 1; a < n; ++a) {
+ if (idx[a] == -1)
+ continue;
+ for (int b = a + 1; b < n; ++b) {
+ if (idx[b] == -1)
+ continue;
+ if (!(a & b)) {
+ int row_a = idx[a];
+ int row_b = idx[b];
+ free(idx);
+ *returnSize = 2;
+ int *ans = (int *)malloc(*returnSize * sizeof(int));
+ ans[0] = fmin(row_a, row_b);
+ ans[1] = fmax(row_a, row_b);
+ return ans;
+ }
+ }
+ }
+ *returnSize = 0;
+ free(idx);
+ return NULL;
+}
+
+int main() {
+ int g1i[3][4] = {{0, 1, 1, 0}, {0, 0, 0, 1}, {1, 1, 1, 1}}, rs1;
+ int g2i[1][1] = {{0}}, rs2;
+ int g3i[2][3] = {{1, 1, 1}, {1, 1, 1}}, rs3;
+ struct two_d_arr g1, g2, g3;
+ two_d_arr_init(&g1, 3, 4, g1i);
+ two_d_arr_init(&g2, 1, 1, g2i);
+ two_d_arr_init(&g3, 2, 3, g3i);
+ int *gsobm1 =
+ goodSubsetofBinaryMatrix(g1.arr, g1.row_size, g1.col_size, &rs1);
+ int *gsobm2 =
+ goodSubsetofBinaryMatrix(g2.arr, g2.row_size, g2.col_size, &rs2);
+ int *gsobm3 =
+ goodSubsetofBinaryMatrix(g3.arr, g3.row_size, g3.col_size, &rs3);
+ for (int i = 0; i < rs1; i++)
+ printf("%d ", gsobm1[i]); // expect: 0 1
+ printf("\n");
+ for (int i = 0; i < rs2; i++)
+ printf("%d ", gsobm2[i]); // expect: 0
+ printf("\n");
+ for (int i = 0; i < rs3; i++)
+ printf("%d ", gsobm3[i]); // expect: null
+ printf("\n");
+ free(gsobm1), two_d_arr_free(&g1);
+ free(gsobm2), two_d_arr_free(&g2);
+ free(gsobm3), two_d_arr_free(&g3);
+}