Complete Competitive-Coding-10

BestTimeBuySellStockII.java

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+// Greedy O(n) time, O(1) space
+class Solution {
+    public int maxProfit(int[] prices) {
+        int maxProfit = 0;
+
+        for (int i = 1; i < prices.length; i++) {
+            if (prices[i] > prices[i-1]) {
+                maxProfit += prices[i] - prices[i-1];
+            }
+        }
+        return maxProfit;
+    }
+}

PeekingIterator.java

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+// Java Iterator interface reference:
+// https://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html
+
+// Brute force O(n) time, O(n) space
+// class PeekingIterator implements Iterator<Integer> {
+
+//     List<Integer> list;
+//     int idx;
+
+// 	public PeekingIterator(Iterator<Integer> iterator) {
+// 	    // initialize any member here.
+// 	    this.list = new ArrayList<>();
+//         this.idx = 0;
+
+//         while (iterator.hasNext()) {
+//             list.add(iterator.next());
+//         }
+// 	}
+
+//     // Returns the next element in the iteration without advancing the iterator.
+// 	public Integer peek() {
+//         return list.get(idx);
+// 	}
+
+// 	// hasNext() and next() should behave the same as in the Iterator interface.
+// 	// Override them if needed.
+// 	@Override
+// 	public Integer next() {
+//         int val = list.get(idx);
+//         idx++;
+// 	    return val;
+// 	}
+
+// 	@Override
+// 	public boolean hasNext() {
+// 	    return idx < list.size();
+// 	}
+// }
+
+
+// O(1) time, O(1) space
+
+import java.util.*;
+
+class PeekingIterator implements Iterator<Integer> {
+
+    Iterator<Integer> itr;
+    Integer nextVal;
+
+	public PeekingIterator(Iterator<Integer> iterator) {
+	    // initialize any member here.
+	    this.itr = iterator;
+        if (itr.hasNext()) {
+            nextVal = itr.next();
+        }
+        else {
+            nextVal = null;
+        }
+	}
+
+    // Returns the next element in the iteration without advancing the iterator.
+	public Integer peek() {
+        return nextVal;
+	}
+
+	// hasNext() and next() should behave the same as in the Iterator interface.
+	// Override them if needed.
+	@Override
+	public Integer next() {
+        Integer temp = nextVal;
+        if (itr.hasNext()) {
+            nextVal = itr.next();
+        }
+        else {
+            nextVal = null;
+        }
+        return temp;
+	}
+
+	@Override
+	public boolean hasNext() {
+	    return nextVal != null;
+	}
+}