update: DP method

Author: hijiangtao

src/best-time-to-buy-and-sell-stock/res.js

@@ -22,4 +22,21 @@ var maxProfit = function(prices) {
 }
 
 return res;
-};
+};
+
+/**
+* DP 解法
+* @param {*} prices
+*/
+var maxProfit_2 = (prices) => {
+if (prices.length < 2) return 0;
+
+let last = 0, max = 0;
+
+for (let i = 1; i < prices.length; i++) {
+last = Math.max(0, last + prices[i] - prices[i-1]);
+max = Math.max(last, max);
+}
+
+return max;
+}