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-rw-r--r--min_domino_rotation_eq_row.c40
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diff --git a/min_domino_rotation_eq_row.c b/min_domino_rotation_eq_row.c
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+++ b/min_domino_rotation_eq_row.c
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+// 1007. Minimum Domino Rotations For Equal Row
+#include "leetcode.h"
+
+/*
+ * in a row of dominoes, 'tops[i]' and 'bottoms[i]' represents the top and
+ * bottom halves of the i'th domino. we may rotate the i'th domino so that
+ * 'tops[i]' and 'bottoms[i]' swap values. return the minimum number of
+ * rotations so that all values in 'tops' are the same, or all values in
+ * 'bottoms' are the same. if it cannot be done, return -1.
+ */
+
+int minDominoRotations(int *tops, int topsSize, int *bottoms, int bottomsSize) {
+ int mask = 0x7E, num = -1, a = 0, b = 0;
+ for (int i = 0; i < topsSize; i++) {
+ mask &= ((1 << tops[i]) | (1 << bottoms[i]));
+ if (!mask)
+ return -1;
+ }
+ while (mask) {
+ num++;
+ mask >>= 1;
+ }
+ for (int i = 0; i < topsSize; i++) {
+ if (tops[i] == num)
+ a++;
+ if (bottoms[i] == num)
+ b++;
+ }
+ int max = a > b ? a : b;
+ return topsSize - max;
+}
+
+int main() {
+ int t1[] = {2, 1, 2, 4, 2, 2}, b1[] = {5, 2, 6, 2, 3, 2};
+ int t2[] = {3, 5, 1, 2, 3}, b2[] = {3, 6, 3, 3, 4};
+ printf("%d\n", minDominoRotations(t1, ARRAY_SIZE(t1), b1,
+ ARRAY_SIZE(b1))); // expect: 2
+ printf("%d\n", minDominoRotations(t2, ARRAY_SIZE(t2), b2,
+ ARRAY_SIZE(b2))); // expect: -1
+}