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/*
reorderBinary.c:
Given a root node, reorder a tree either as postorder or preorder.
Works only on binary trees, in which each internal node has exactly 2
descendants. Function inputs are derived from a phylo4 edge matrix.
The new descendant node ordering is stored in descendantNew.
*/
#include <R.h>
typedef struct {
int *descendantNew;
int *ancestor;
int *left;
int *right;
int nEdges;
int index;
} tree;
void postorderBinary(tree*, int node);
void preorderBinary(tree*, int node);
void reorderBinary(int *descendantNew, int *root, int *ancestor, int *left,
int *right, int *nEdges, int *order) {
tree tr;
tr.ancestor = ancestor;
tr.left = left;
tr.right = right;
tr.descendantNew = descendantNew;
tr.nEdges = *nEdges;
tr.index = 0;
if (*order==0) {
postorderBinary(&tr, *root);
} else if (*order==1) {
preorderBinary(&tr, *root);
} else {
error("invalid order type");
}
}
// postorder: continue traversing to the end, then record node
void postorderBinary(tree *tr, int node) {
for (int i=0; i<tr->nEdges; i++) {
if (tr->ancestor[i]==node) {
postorderBinary(tr, tr->left[i]);
postorderBinary(tr, tr->right[i]);
}
}
tr->descendantNew[tr->index] = node;
tr->index += 1;
}
// preorder: record node first, then continue traversing
void preorderBinary(tree *tr, int node) {
tr->descendantNew[tr->index] = node;
tr->index += 1;
for (int i=0; i<tr->nEdges; i++) {
if (tr->ancestor[i]==node) {
preorderBinary(tr, tr->left[i]);
preorderBinary(tr, tr->right[i]);
}
}
}
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