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[LeetCode: reverse a string] ( NSString* reverseString(NSString *originalString) { // use a new string to append the chars from the old one NSString *newString = @""; for (int i =

BOOL checkDuplicates(NSString *str) { NSMutableArray *storageArray = [NSMutableArray array]; for (int i = 0; i < str.length; i++) { NSString *charStr = [str substringWithRange:NSMakeRange(i,1)]; if

LeetCode Convert Sorted Array to Binary Search Tree in Objective C typedef struct { int value; struct TreeNode *left; struct TreeNode *right; } TreeNode; -(TreeNode *)sortedArrayToBST:(NSArray *array)

LeetCode: Validate Binary Search Tree in Objective C typedef struct { int value; struct TreeNode *left; struct TreeNode *right; } TreeNode; -(BOOL)isValidBST:(TreeNode *)node { return (valid:node

LeetCode: Balanced Binary Tree in Objective C typedef struct { int value; struct TreeNode *left; struct TreeNode *right; } TreeNode; - (BOOL)isBalanced:(TreeNode *)node { if (!node) return true; return

LeetCode: Maximum Depth of Binary Tree in Objective C typedef struct { int value; struct TreeNode *left; struct TreeNode *right; } TreeNode; - (int)maximumDepth:(TreeNode *)node { if (!node) return 0;

typedef struct { int value; struct TreeNode *left; struct TreeNode *right; } TreeNode; -(NSMutableArray *)levelOrder:(TreeNode *)treeNode { NSMutableArray *levelOrderArray = [NSMutableArray array]; if

// typedef struct { // int value; // struct TreeNode *left; // struct TreeNode *right; // } TreeNode; -(NSMutableArray *)preorderTraversal:(TreeNode *)treeNode { NSMutableArray *preorderArray = [NSMutableArray