Create HIndex.java

274

Author: leo414

HIndex.java

@@ -0,0 +1,46 @@
+package leetcode;
+
+import java.util.Arrays;
+
+/**
+ * Project Name : Leetcode
+ * Package Name : leetcode
+ * File Name : HIndex
+ * Creator : Leo
+ * Description : 274. H-Index
+ */
+public class HIndex {
+    /**
+     * For example, given citations = [3, 0, 6, 1, 5], which means the researcher has 5 papers in total
+     * and each of them had received 3, 0, 6, 1, 5 citations respectively. Since the researcher has 3 papers with at
+     * least 3 citations each and the remaining two with no more than 3 citations each, his h-index is 3.
+
+     * 0 1 2 3 4
+     * 6 5 3 1 0
+     */
+    // time : O(nlogn) space : O(1)
+    public int hIndex(int[] citations) {
+        Arrays.sort(citations);
+        int res = 0;
+        while (res < citations.length && citations[citations.length - 1 - res] > res) {
+            res++;
+        }
+        return res;
+    }
+
+    // time : O(n) space : O(n)
+    public int hIndex2(int[] citations) {
+        int[] helper = new int[citations.length + 1];
+        for (int i = 0; i < citations.length; i++) {
+            helper[citations[i] <= citations.length ? citations[i] : citations.length] += 1;
+        }
+        int sum = 0;
+        for (int i = citations.length; i > 0; i--) {
+            sum += helper[i];
+            if (sum >= i) {
+                return i;
+            }
+        }
+        return 0;
+    }
+}