add Easy_268_Missing_Number

zongyanqi · zongyanqi · commit 4aba7a613f1a · 2017-03-13T23:27:24.000+08:00
diff --git a/Easy_268_Missing_Number.js b/Easy_268_Missing_Number.js
@@ -0,0 +1,30 @@
+/**
+ *
+ * Given an array containing n distinct numbers taken from 0, 1, 2, ..., n,
+ * find the one that is missing from the array.
+ * For example,
+ * Given nums = [0, 1, 3] return 2.
+ *
+ * Note:
+ * Your algorithm should run in linear runtime complexity.
+ * Could you implement it using only constant extra space complexity?
+ *
+ *
+ */
+
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var missingNumber = function (nums) {
+    var n = nums.length;
+    var ideal = n * (n + 1) / 2;
+    var sum = nums.reduce((a, b)=> a = a + b, 0);
+    return ideal - sum;
+};
+
+console.log(missingNumber([0, 1, 3]) == 2);
+console.log(missingNumber([0, 1, 2]) == 3);
+console.log(missingNumber([1, 2, 3, 4]) == 0);
+
+
