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-rw-r--r--avoid_flood_city.c123
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diff --git a/avoid_flood_city.c b/avoid_flood_city.c
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+// 1488. Avoid Flood in The City
+#include "leetcode.h"
+
+/*
+ * your country has an infinite number of lakes. initially, all the lakes are
+ * empty. but when it rains over the n'th lake, the n'th lake becomes full of
+ * water. if it rains over a lake that is full of water, there will be a flood.
+ * your goal is to avoid any floods. if there are multiple valid answers, return
+ * any of them. if it is impossible to avoid flood, return an empty array.
+ * notice that if yo uchose to dry a full lake, it becomes empty. but if you
+ * chose to dry an empty lake, nothing happens.
+ */
+
+#define HASH_SIZE 200003
+
+struct hash_entry {
+ int key;
+ int val;
+ bool used;
+};
+
+int hash_func(int key) {
+ if (key < 0)
+ key = -key;
+ return key % HASH_SIZE;
+}
+
+int *hash_get(struct hash_entry *obj, int key) {
+ int hash = hash_func(key);
+ while (obj[hash].used) {
+ if (obj[hash].key == key)
+ return &obj[hash].val;
+ hash++;
+ if (hash == HASH_SIZE)
+ hash = 0;
+ }
+ return NULL;
+}
+
+int *hash_put(struct hash_entry *obj, int key, int val) {
+ int hash = hash_func(key);
+ while (obj[hash].used) {
+ if (obj[hash].key == key) {
+ obj[hash].val = val;
+ return &obj[hash].val;
+ }
+ hash++;
+ if (hash == HASH_SIZE)
+ hash = 0;
+ }
+ obj[hash].used = true;
+ obj[hash].key = key;
+ obj[hash].val = val;
+ return &obj[hash].val;
+}
+
+int dry_day(int *dry_days, int dry_cnt, int target) {
+ int low = 0, high = dry_cnt - 1, res = -1;
+ while (low <= high) {
+ int mid = low + (high - low) / 2;
+ if (dry_days[mid] > target) {
+ res = mid;
+ high = mid - 1;
+ } else
+ low = mid + 1;
+ }
+ return res;
+}
+
+int *avoidFlood(int *rains, int rainsSize, int *returnSize) {
+ *returnSize = rainsSize;
+ int *ans = (int *)malloc(rainsSize * sizeof(int));
+ int *dry = (int *)malloc(rainsSize * sizeof(int));
+ int dry_cnt = 0;
+ struct hash_entry *hash_table =
+ (struct hash_entry *)calloc(HASH_SIZE, sizeof(struct hash_entry));
+ for (int i = 0; i < rainsSize; i++) {
+ if (!rains[i]) {
+ dry[dry_cnt++] = i;
+ ans[i] = 1;
+ } else {
+ int *prev = hash_get(hash_table, rains[i]);
+ if (prev) {
+ int idx = dry_day(dry, dry_cnt, *prev);
+ if (idx == -1) {
+ free(ans);
+ free(dry);
+ free(hash_table);
+ *returnSize = 0;
+ return NULL;
+ }
+ int day = dry[idx];
+ ans[day] = rains[i];
+ memmove(dry + idx, dry + idx + 1, (dry_cnt - idx - 1) * sizeof(int));
+ dry_cnt--;
+ }
+ hash_put(hash_table, rains[i], i);
+ ans[i] = -1;
+ }
+ }
+ free(dry);
+ free(hash_table);
+ return ans;
+}
+
+int main() {
+ int r1[] = {1, 2, 3, 4}, r2[] = {1, 2, 0, 0, 2, 1}, r3[] = {1, 2, 0, 1, 2};
+ int rs1, *af1 = avoidFlood(r1, ARRAY_SIZE(r1), &rs1);
+ int rs2, *af2 = avoidFlood(r2, ARRAY_SIZE(r2), &rs2);
+ int rs3, *af3 = avoidFlood(r3, ARRAY_SIZE(r3), &rs3);
+ for (int i = 0; i < rs1; i++)
+ printf("%d ", af1[i]); // expect: -1 -1 -1 -1
+ printf("\n");
+ for (int i = 0; i < rs2; i++)
+ printf("%d ", af2[i]); // expect: -1 -1 2 1 -1 -1
+ printf("\n");
+ for (int i = 0; i < rs3; i++)
+ printf("%d ", af3[i]); // expect: null
+ printf("\n");
+ free(af1);
+ free(af2);
+ free(af3);
+}