Javascript Interview Question Tree Binary Tree Get ancestor

Introduction

Find the lowest common ancestor of a binary search tree, given two nodes.

You may assume that both nodes are members of the tree. 

function Node(left, right, value) {
    this.left = left;/*from w  ww .  j  a va2  s  . c o m*/
    this.right = right;
    this.value = value;
}


var root = new Node(
    new Node(
        new Node(null, null, 28),
        new Node(null, null, 79),
        62
    ),
    new Node(
        new Node(
            new Node(null, null, 121),
            null,
            130),
        new Node(null, null, 190),
        141
    ),
    110
);

function findLowestCommonAncestor(root, value1, value2) {
    //your code
}
console.log( findLowestCommonAncestor(root, 121, 190) );
console.log( findLowestCommonAncestor(root, 28 , 190) );
console.log( findLowestCommonAncestor(root, 28 , 79 ) );
console.log( findLowestCommonAncestor(root, 62 , 141) );




/**
 * @class {public} Node
 *
 * A typical binary tree node.
 *
 * @param {Node} left - the left node.
 * @param {Node} right - the right node.
 * @param {Integer} value - the value of this node.
 */
function Node(left, right, value) {
    this.left = left;
    this.right = right;
    this.value = value;
}

/*
 * Sample tree structure.
 */
var root = new Node(
    new Node(
        new Node(null, null, 28),
        new Node(null, null, 79),
        62
    ),
    new Node(
        new Node(
            new Node(null, null, 121),
            null,
            130),
        new Node(null, null, 190),
        141
    ),
    110
);

/**
 * @function {public static} findLowestCommonAncestor
 *
 * Finds the lowest common ancestor between two nodes.
 *
 * @param {Node} root - the root node.
 * @param {Integer} value1 - the left value.
 * @param {Integer} value2 - the right value.
 *
 * @return the found node, if any; `null` otherwise.
 */
function findLowestCommonAncestor(root, value1, value2) {
    var current = root;
    var value = null;

    while (current != null) {
        value = current.value;

        if (value > value1 && value > value2) {
            current = current.left;
        } else if (value < value1 && value < value2) {
            current = current.right;
        } else {
            return current;
        }
    }

    return null;
}
console.log( findLowestCommonAncestor(root, 121, 190) );
console.log( findLowestCommonAncestor(root, 28 , 190) );
console.log( findLowestCommonAncestor(root, 28 , 79 ) );
console.log( findLowestCommonAncestor(root, 62 , 141) );

/*
Output: ($ /usr/bin/node 008.js)

{ left:
   { left: { left: null, right: null, value: 121 },
     right: null,
     value: 130 },
  right: { left: null, right: null, value: 190 },
  value: 141 }
{ left:
   { left: { left: null, right: null, value: 28 },
     right: { left: null, right: null, value: 79 },
     value: 62 },
  right:
   { left: { left: [Object], right: null, value: 130 },
     right: { left: null, right: null, value: 190 },
     value: 141 },
  value: 110 }
{ left: { left: null, right: null, value: 28 },
  right: { left: null, right: null, value: 79 },
  value: 62 }
{ left:
   { left: { left: null, right: null, value: 28 },
     right: { left: null, right: null, value: 79 },
     value: 62 },
  right:
   { left: { left: [Object], right: null, value: 130 },
     right: { left: null, right: null, value: 190 },
     value: 141 },
  value: 110 }
*/



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