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-rw-r--r--russian_doll_envelopes.c60
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diff --git a/russian_doll_envelopes.c b/russian_doll_envelopes.c
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+// 354. Russian Doll Envelopes
+#include "leetcode.h"
+
+/*
+ * you are given a 2d array of integers 'envelopes' where 'envelopes[i] = [w_i,
+ * h_i]' represents the width and height of an envelope. one envelope can fit
+ * into another if and only if both the width and height of one envelope are
+ * greater than the other envelope's width and height. return the maximum number
+ * of envelopes you can russian doll (ie. put one inside the other).
+ */
+
+int bin_search(int *dp, int start, int end, int target) {
+ while (start < end) {
+ int mid = start + (end - start) / 2;
+ if (dp[mid] == target)
+ return mid;
+ else if (dp[mid] > target)
+ end = mid;
+ else
+ start = mid + 1;
+ }
+ return start;
+}
+
+int cmp(const void *a, const void *b) {
+ if ((*(int **)a)[0] == (*(int **)b)[0])
+ return (*(int **)b)[1] - (*(int **)a)[1];
+ else
+ return (*(int **)a)[0] - (*(int **)b)[0];
+}
+
+int maxEnvelopes(int **envelopes, int envelopesSize, int *envelopesColSize) {
+ qsort(envelopes, envelopesSize, sizeof(int **), cmp);
+ int *dp = (int *)malloc(envelopesSize * sizeof(int)), ans = 0;
+ dp[0] = envelopes[0][1];
+ for (int i = 1; i < envelopesSize; i++) {
+ if (envelopes[i][1] > dp[ans - 1])
+ dp[ans++] = envelopes[i][1];
+ else {
+ int idx = bin_search(dp, 0, ans, envelopes[i][1]);
+ dp[idx] = envelopes[i][1];
+ if (idx == ans)
+ ans++;
+ }
+ }
+ free(dp);
+ return ans;
+}
+
+int main() {
+ int e1i[4][2] = {{5, 4}, {6, 4}, {6, 7}, {2, 3}},
+ e2i[3][2] = {{1, 1}, {1, 1}, {1, 1}};
+ struct two_d_arr e1, e2;
+ two_d_arr_init(&e1, ARRAY_SIZE(e1i), ARRAY_SIZE(e1i[0]), e1i);
+ two_d_arr_init(&e2, ARRAY_SIZE(e2i), ARRAY_SIZE(e2i[0]), e2i);
+ printf("%d\n", maxEnvelopes(e1.arr, e1.row_size, e1.col_size)); // expect: 3
+ printf("%d\n", maxEnvelopes(e2.arr, e2.row_size, e2.col_size)); // expect: 1
+ two_d_arr_free(&e1);
+ two_d_arr_free(&e2);
+}