add code of 121

Author: Li Li

Algorithms Basics/top-interview-questions/121. Best Time to Buy and Sell Stock.cs

@@ -0,0 +1,18 @@
+// mantain two value: minPrice, maxProfit
+public class Solution {
+    public int MaxProfit(int[] prices) {
+        if (prices == null || prices.Length < 2) {
+            return 0;
+        }
+        int minPrice = prices[0];
+        int maxProfit = 0;
+        for (int i = 1; i < prices.Length; i++) {
+            if (prices[i] < minPrice) {
+                minPrice = prices[i];
+            } else if (prices[i] - minPrice > maxProfit) {
+                maxProfit = prices[i] - minPrice;
+            }
+        }
+        return maxProfit;
+    }
+}