Completed Competitive-Coding-10

BuyAndSellStock2.java

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+// Time Complexity : O(n)
+// Space Complexity : O(1)
+// Did this code successfully run on Leetcode : yes
+// Any problem you faced while coding this : no
+
+// Your code here along with comments explaining your approach
+/*
+If the incoming price is greater than the previous price, we append the difference of prices to the existing
+profit. This way, we can maximize the total profit accumulated.
+ */
+class Solution {
+    public int maxProfit(int[] prices) {
+        int profit = 0;
+        for(int i = 1 ; i < prices.length ; i++) {
+            if(prices[i] > prices[i - 1]) {
+                profit += prices[i] - prices[i - 1];
+            }
+        }
+        return profit;
+    }
+}

PeekingIterator.java

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+// Time Complexity : O(1)
+// Space Complexity : O(1)
+// Did this code successfully run on Leetcode : yes
+// Any problem you faced while coding this : no
+
+// Your code here along with comments explaining your approach
+/*
+We create a new iterator on top of the existing iterator and assign it. We also maintain a nextElement which
+helps us get the next value of our iterator.Both the peek and hasNext methods can be implemented using this
+nextElement presence. For next method, we get the current nextElement and return it and before we return, we
+make it increment to next element of the iterator if applicable, or else, make it null.
+ */
+
+// Java Iterator interface reference:
+// https://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html
+
+class PeekingIterator implements Iterator<Integer> {
+    Iterator<Integer> itr;
+    Integer nextEl;
+
+    public PeekingIterator(Iterator<Integer> iterator) {
+        // initialize any member here.
+        this.itr = iterator;
+        nextEl = itr.next();
+    }
+
+    // Returns the next element in the iteration without advancing the iterator.
+    public Integer peek() {
+        return nextEl;
+    }
+
+    // hasNext() and next() should behave the same as in the Iterator interface.
+    // Override them if needed.
+    @Override
+    public Integer next() {
+        Integer temp = nextEl;
+        nextEl = null;
+        if(itr.hasNext()) {
+            nextEl = itr.next();
+        }
+        return temp;
+    }
+
+    @Override
+    public boolean hasNext() {
+        return nextEl != null;
+    }
+}