Adding all the solutions

best-time-to-buy-and-sell-stock-ii.java

@@ -0,0 +1,15 @@
+// TimeComplexity: O(n)
+// SpaceComplexity: O(1)
+// Explanation: I am solving the problem by adding all positive price differences between consecutive days. If the price on the next day is higher than the current day, I add the difference to the total profit because it represents a valid buy and sell opportunity. This approach works because multiple small profitable transactions are equivalent to one larger transaction in terms of total profit.
+
+class Solution {
+    public int maxProfit(int[] prices) {
+        int profit =0;
+        for(int i=0; i<prices.length-1; i++) {
+            if(prices[i]<prices[i+1]) {
+                profit = profit + prices[i+1] - prices[i];
+            }
+        }
+        return profit;
+    }
+}

peeking-iterator.java

@@ -0,0 +1,50 @@
+//  TimeComplexity : O(1)
+//  SpaceComplexity : O(1)
+// Java Iterator interface reference:
+// https://docs.oracle.com/javase/8/docs/api/java/util/Iterator.html
+
+class PeekingIterator implements Iterator<Integer> {
+    private Integer nextEl;
+    private Iterator<Integer> iter;
+	public PeekingIterator(Iterator<Integer> iterator) {
+	    // initialize any member here.
+        this.iter = iterator;
+        if (iterator.hasNext()) {
+            this.nextEl = iterator.next();
+        }   
+	}
+
+    // Returns the next element in the iteration without advancing the iterator.
+    // TimeComplexity: O(1)
+    // SpcaeComplexity: O(1)
+	public Integer peek() {
+        return this.nextEl;
+
+	}
+
+	// hasNext() and next() should behave the same as in the Iterator interface.
+	// Override them if needed.
+    // TimeComplexity: O(1)
+    // SpcaeComplexity: O(1)
+	@Override
+	public Integer next() {
+
+        Integer result = nextEl;
+
+        if (iter.hasNext()) {
+            nextEl = iter.next();
+        } else {
+            nextEl = null;
+        }
+
+        return result;  
+	}
+
+	@Override
+    // TimeComplexity: O(1)
+    // SpcaeComplexity: O(1)
+	public boolean hasNext() {
+        return (this.nextEl!=null);
+
+	}
+}