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‫So now we're going to do our introduction to depth first search in order.

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‫So I'm going to bring up a tree and with depth first search in order, we're going to start at the root

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‫and we're going to visit this node and then we're going to go left and visit the 21 node, and we're

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‫going to go left again and visit the 18 node.

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‫Now, so far, this looks just like depth first search post order, but there is a small change with

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‫post order.

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‫We looked left and then looked right and then printed out the value of the 18 node.

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‫With an order.

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‫We're going to look left.

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‫We're going to print out the value, so I'm going to colour that in.

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‫Then we look right.

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‫So now we come back up to the 21 node.

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‫It has looked left.

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‫Now it's going to print its value and then it goes right to the 27 node.

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‫It looks left.

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‫It prints this value.

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‫It looks right now.

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‫We come all the way back up to the 47 node.

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‫It has looked left.

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‫Now it will print its value.

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‫Then go right to the 76 node.

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‫The 76 node will go left to the 52.

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‫It will look left.

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‫It will print its value look right.

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‫We come back up to the 76.

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‫It already went left.

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‫It will print its value and go right.

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‫The 82 node will look left.

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‫It will print its value and then look right.

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‫So I'm going to put the tree back the way it was and just show the order that the numbers are output.

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‫They are output in numerical order.

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‫We started with the 18 and then did 21, 27, 47, 52, 76 and 82.

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‫Hence the name depth for search in order.