Added more solutions to easy category

Author: kanahaiya

LeetCodeSolutions/EasyLevelSolutions/src/main/java/com/javaaid/solutions/easy/dp/BestTimeToBuyAndSellStock.java

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+/**
+ * 
+ */
+package com.javaaid.solutions.easy.dp;
+
+/**
+ * @author Kanahaiya Gupta
+ *
+ */
+public class BestTimeToBuyAndSellStock {
+	public int maxProfit(int[] prices) {
+		int max_so_far = 0, curr_max = 0;
+		for (int i = 1; i < prices.length; i++) {
+			curr_max += prices[i] - prices[i - 1];
+			curr_max = Math.max(curr_max, 0);
+			max_so_far = Math.max(max_so_far, curr_max);
+		}
+		return max_so_far;
+	}
+}

LeetCodeSolutions/EasyLevelSolutions/src/main/java/com/javaaid/solutions/easy/dp/ClimbingStairs.java

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+/**
+ * 
+ */
+package com.javaaid.solutions.easy.dp;
+
+/**
+ * @author Kanahaiya Gupta
+ *
+ */
+public class ClimbingStairs {
+	public int climbStairs(int n) {
+		int dp[] = new int[n + 1];
+		return climbStairsUtil(n, dp);
+
+	}
+
+	public int climbStairsUtil(int n, int[] dp) {
+		if (n < 0)
+			return 0;
+		if (n == 0)
+			return 1;
+		if (dp[n] != 0) {
+			return dp[n];
+		} else {
+			return dp[n] = climbStairsUtil(n - 1, dp) + climbStairsUtil(n - 2, dp);
+		}
+
+	}
+}

LeetCodeSolutions/EasyLevelSolutions/src/main/java/com/javaaid/solutions/easy/dp/HouseRobber.java

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+/**
+ * 
+ */
+package com.javaaid.solutions.easy.dp;
+
+/**
+ * @author Kanahaiya Gupta
+ *
+ */
+public class HouseRobber {
+	public int rob(int[] nums) {
+		int n = nums.length;
+		if (n == 0)
+			return 0;
+		if (n == 1)
+			return nums[0];
+
+		int dp[] = new int[n + 1];
+		dp[0] = nums[0];
+		dp[1] = Math.max(dp[1], dp[0]);
+		int max = dp[1];
+		for (int i = 2; i < n; i++) {
+			dp[i] = Math.max(dp[i - 1], dp[i - 2] + nums[i]);
+			max = Math.max(max, dp[i]);
+		}
+		return max;
+	}
+}

LeetCodeSolutions/EasyLevelSolutions/src/main/java/com/javaaid/solutions/easy/dp/MaximumProductSubarray.java

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+/**
+ * 
+ */
+package com.javaaid.solutions.easy.dp;
+
+/**
+ * @author Kanahaiya Gupta
+ *
+ */
+public class MaximumProductSubarray {
+	public int maxProduct(int[] nums) {
+		int max_so_far = 1, max_ending_here = 1;
+		for (int i = 0; i < nums.length; i++) {
+			max_ending_here *= nums[i];
+			max_ending_here = Math.max(max_ending_here, nums[i]);
+			max_so_far = Math.max(max_so_far, max_ending_here);
+		}
+		return max_so_far;
+	}
+}

LeetCodeSolutions/EasyLevelSolutions/src/main/java/com/javaaid/solutions/easy/dp/MaximumSubarray.java

@@ -0,0 +1,20 @@
+/**
+ * 
+ */
+package com.javaaid.solutions.easy.dp;
+
+/**
+ * @author Kanahaiya Gupta
+ *
+ */
+public class MaximumSubarray {
+	public int maxSubArray(int[] nums) {
+        int max_so_far=Integer.MIN_VALUE,max_ending_here=0;
+        for(int i=0;i<nums.length;i++){
+            max_ending_here+=nums[i];
+            max_ending_here=Math.max(max_ending_here,nums[i]);
+            max_so_far=Math.max(max_so_far,max_ending_here);
+        }
+     return max_so_far;   
+    }
+}

LeetCodeSolutions/EasyLevelSolutions/src/main/java/com/javaaid/solutions/easy/dp/MinCostClimbingStairs.java

@@ -0,0 +1,21 @@
+/**
+ * 
+ */
+package com.javaaid.solutions.easy.dp;
+
+/**
+ * @author Kanahaiya Gupta
+ *
+ */
+public class MinCostClimbingStairs {
+public int minCostClimbingStairs(int[] cost) {
+	int n=cost.length;
+     int[] dp=new int[cost.length+1];
+     dp[0]=cost[0];
+     dp[1]=cost[1];
+	for(int i=2;i<cost.length;i++) {
+		dp[i]=cost[i]+Math.min(dp[i-1], dp[i-2]);
+	}
+	return Math.min(dp[n-2], dp[n-1]);
+    }
+}

LeetCodeSolutions/EasyLevelSolutions/src/main/java/com/javaaid/solutions/easy/dp/RangeSumQueryImmutable.java

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+/**
+ * 
+ */
+package com.javaaid.solutions.easy.dp;
+
+/**
+ * @author Kanahaiya Gupta
+ *
+ */
+public class RangeSumQueryImmutable {
+
+	int[] nums;
+
+	public RangeSumQueryImmutable(int[] nums) {
+		this.nums = nums;
+		for (int k = 1; k < nums.length; k++) {
+			nums[k] += nums[k - 1];
+		}
+
+	}
+
+	public int sumRange(int i, int j) {
+
+		if (i > 0)
+			return (nums[j] - nums[i - 1]);
+		return (nums[j]);
+	}
+}

LeetCodeSolutions/EasyLevelSolutions/src/main/java/com/javaaid/solutions/easy/trees/ConvertSortedArrayToBinarySearchTree.java

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+/**
+ * 
+ */
+package com.javaaid.solutions.easy.trees;
+
+/**
+ * @author Kanahaiya Gupta
+ *
+ */
+public class ConvertSortedArrayToBinarySearchTree {
+	static class TreeNode {
+		int val;
+		TreeNode left;
+		TreeNode right;
+
+		TreeNode(int x) {
+			val = x;
+		}
+	}
+
+	public TreeNode sortedArrayToBST(int[] nums) {
+		TreeNode root = null;
+		root = sortedArrayToBSTUtil(nums, 0, nums.length - 1);
+		return root;
+	}
+
+	/**
+	 * 
+	 * @param nums
+	 * @param start
+	 * @param end
+	 * @return
+	 */
+	private TreeNode sortedArrayToBSTUtil(int[] nums, int start, int end) {
+		if (start > end) {
+			return null;
+		}
+		int mid = (start + end) / 2;
+		TreeNode node = new TreeNode(nums[mid]);
+		node.left = sortedArrayToBSTUtil(nums, start, mid - 1);
+		node.right = sortedArrayToBSTUtil(nums, mid + 1, end);
+		return node;
+	}
+}