diff --git a/121_best_time_to_buy_and_sell_stock/stock.c b/121_best_time_to_buy_and_sell_stock/stock.c
index a960599..b711785 100644
--- a/121_best_time_to_buy_and_sell_stock/stock.c
+++ b/121_best_time_to_buy_and_sell_stock/stock.c
@@ -3,12 +3,19 @@
 
 static int maxProfit(int* prices, int pricesSize)
 {
-    int i, j, diff = 0;
-    for (i = 0; i < pricesSize; i++) {
-        for (j = i + 1; j < pricesSize; j++) {
-            diff = prices[j] - prices[i] > diff ? prices[j] - prices[i] : diff;
+    if (pricesSize == 0) {
+        return 0;
+    }
+
+    int i, diff = 0, min = prices[0];
+    for (i = 1; i < pricesSize; i++) {
+        if (prices[i] < min) {
+            min = prices[i];
+        } else {
+            diff = prices[i] - min > diff ? prices[i] - min : diff;
         }
     }
+
     return diff;
 }
 
diff --git a/122_best_time_to_buy_and_sell_stock_ii/Makefile b/122_best_time_to_buy_and_sell_stock_ii/Makefile
new file mode 100644
index 0000000..c638fbb
--- /dev/null
+++ b/122_best_time_to_buy_and_sell_stock_ii/Makefile
@@ -0,0 +1,2 @@
+all:
+	gcc -O2 -o test stock.c
diff --git a/122_best_time_to_buy_and_sell_stock_ii/stock.c b/122_best_time_to_buy_and_sell_stock_ii/stock.c
new file mode 100644
index 0000000..8c53220
--- /dev/null
+++ b/122_best_time_to_buy_and_sell_stock_ii/stock.c
@@ -0,0 +1,24 @@
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdbool.h>
+#include <string.h>
+
+static int maxProfit(int* prices, int pricesSize)
+{
+    int i, j, total = 0;
+    for (i = 1; i < pricesSize; i++) {
+        total += prices[i] > prices[i - 1] ? prices[i] - prices[i - 1] : 0;
+    }
+    return total;
+}
+
+int main(int argc, char **argv)
+{
+    int i, count = argc - 1;
+    int *nums = malloc(count * sizeof(int));
+    for (i = 0; i < count; i++) {
+        nums[i] = atoi(argv[i + 1]);
+    }
+    printf("%d\n", maxProfit(nums, count));
+    return 0;
+}