Given a BST, find 2 nodes in it which sum to a given target
hint:
Inorder traversal + BST + 2 SUM
* Time : O(N)
* Space: O(lgN)
1 class TreeNode0 { 2 int val; 3 TreeNode0 left, right; 4 public TreeNode0(int val) { 5 this.val = val; 6 } 7 } 8 public class BST2sum { 9 public void bst2sum(TreeNode0 root, int target) { 10 TreeNode0 left = root, right = root; 11 TreeNode0 curl = root, curr = root; 12 Stack<TreeNode0> stack0 = new Stack<TreeNode0>(); 13 Stack<TreeNode0> stack1 = new Stack<TreeNode0>(); 14 /* 15 * Init, find the most-left and most-right node 16 */ 17 while (curl != null || !stack0.isEmpty()) { 18 if (curl != null) { 19 stack0.push(curl); 20 curl = curl.left; 21 } else { 22 curl = stack0.pop(); 23 left = curl; 24 curl = curl.right; 25 break; 26 } 27 } 28 while (curr != null || !stack1.isEmpty()) { 29 if (curr != null) { 30 stack1.push(curr); 31 curr = curr.right; 32 } else { 33 curr = stack1.pop(); 34 right = curr; 35 curr = curr.left; 36 break; 37 } 38 } 39 while (right.val >= left.val) { 40 System.out.println("left: "+left.val + ", right: "+right.val); 41 if (left.val + right.val == target) { 42 System.out.println(left.val + ", " + right.val); 43 return; 44 } else if (left.val + right.val < target) { // move left 45 while (curl != null || !stack0.isEmpty()) { 46 if (curl != null) { 47 stack0.push(curl); 48 curl = curl.left; 49 } else { 50 curl = stack0.pop(); 51 left = curl; 52 curl = curl.right; 53 break; 54 } 55 } 56 } else if (left.val + right.val > target) { // move right 57 while (curr != null || !stack1.isEmpty()) { 58 if (curr != null) { 59 stack1.push(curr); 60 curr = curr.right; 61 } else { 62 curr = stack1.pop(); 63 right = curr; 64 curr = curr.left; 65 break; 66 } 67 } 68 } 69 } 70 System.out.println("the target has not been found"); 71 } 72 public static void main(String[] args) { 73 TreeNode0 node0 = new TreeNode0(0); 74 TreeNode0 node1 = new TreeNode0(3); 75 TreeNode0 node2 = new TreeNode0(5); 76 TreeNode0 node3 = new TreeNode0(6); 77 TreeNode0 node4 = new TreeNode0(7); 78 TreeNode0 node5 = new TreeNode0(9); 79 TreeNode0 node6 = new TreeNode0(13); 80 TreeNode0 node7 = new TreeNode0(17); 81 TreeNode0 node8 = new TreeNode0(22); 82 TreeNode0 node9 = new TreeNode0(23); 83 node4.left = node2; 84 node4.right = node6; 85 node6.left = node5; 86 node6.right = node8; 87 node8.left = node7; 88 node8.right = node9; 89 node2.left = node0; 90 node2.right = node3; 91 node0.right = node1; 92 BST2sum tree = new BST2sum(); 93 tree.bst2sum(node4, 11); 94 tree.bst2sum(node4, 15); 95 tree.bst2sum(node4, 18); 96 tree.bst2sum(node4, 30); 97 } 98 } 99 /* 100 7 101 / 102 5 13 103 / \ / 104 0 6 9 22 105 \ / 106 3 17 23 107 */
时间: 2024-11-07 18:43:41