add 188

fishercoder1534 · fishercoder1534 · commit b9d454958df6 · 2017-06-08T21:47:48.000-07:00
diff --git a/README.md b/README.md
@@ -341,6 +341,7 @@ Your ideas/fixes/algorithms are more than welcome!
 |191|[Number of 1 Bits](https://leetcode.com/problems/number-of-1-bits/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_191.java)| O(n)|O(1)| Easy | Bit Manipulation
 |190|[Reverse Bits](https://leetcode.com/problems/reverse-bits/)|[Solution](../master/src/main/java/com/fishercoder/solutions/ReverseBits.java)| O(n)|O(1)| Easy | Bit Manipulation
 |189|[Rotate Array](https://leetcode.com/problems/rotate-array/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_189.java)| O(n)|O(n), could be optimized to O(1) | Easy
+|188|[Best Time to Buy and Sell Stock IV](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-iv/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_188.java)| O(n*k)|O(n*k) | Hard | DP
 |187|[Repeated DNA Sequences](https://leetcode.com/problems/repeated-dna-sequences/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_187.java)| O(n)|O(n) | Medium
 |186|[Reverse Words in a String II](https://leetcode.com/problems/reverse-words-in-a-string-ii/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_186.java)| O(n)|O(1)| Medium
 |179|[Largest Number](https://leetcode.com/problems/largest-number/)|[Queue](../master/src/main/java/com/fishercoder/solutions/BSTIterator_using_q.java) [Stack](../../blmaster/MEDIUM/src/medium/LargestNumber.java)| O(?) |O(?) | Medium|
diff --git a/src/main/java/com/fishercoder/solutions/_188.java b/src/main/java/com/fishercoder/solutions/_188.java
@@ -0,0 +1,41 @@
+package com.fishercoder.solutions;
+
+/**
+ * 188. Best Time to Buy and Sell Stock IV
+ *
+ * Say you have an array for which the ith element is the price of a given stock on day i.
+
+ Design an algorithm to find the maximum profit. You may complete at most k transactions.
+
+ Note:
+ You may not engage in multiple transactions at the same time (ie, you must sell the stock before you buy again).
+ */
+public class _188 {
+
+    /**credit: https://discuss.leetcode.com/topic/8984/a-concise-dp-solution-in-java*/
+    public int maxProfit(int k, int[] prices) {
+        int len = prices.length;
+        if (k >= len / 2) return quickSolve(prices);
+
+        int[][] t = new int[k + 1][len];
+        for (int i = 1; i <= k; i++) {
+            int tmpMax =  -prices[0];
+            for (int j = 1; j < len; j++) {
+                t[i][j] = Math.max(t[i][j - 1], prices[j] + tmpMax);
+                tmpMax =  Math.max(tmpMax, t[i - 1][j - 1] - prices[j]);
+            }
+        }
+        return t[k][len - 1];
+    }
+
+
+    private int quickSolve(int[] prices) {
+        int len = prices.length, profit = 0;
+        for (int i = 1; i < len; i++) {
+            // as long as there is a price gap, we gain a profit.
+            if (prices[i] > prices[i - 1]) profit += prices[i] - prices[i - 1];
+        }
+        return profit;
+    }
+
+}
