First Order + middle order and middle order + post order creation

Idea: the first element in the first and last elements in the latter order are the root of the current subtree, and then traverse the middle sequence to find the line between the left and right subtree, recursively create left and right subtree.

Class solution {public:/* because it is OJ, it is assumed that the given sequence is legal, normally, you need to determine the illegal situation */treenode * buildtree (vector <int> & inorder, vector <int> & postorder, int instart, int inend, int poststart, int postend) {treenode * root = new treenode (postorder [postend]); If (instart = inend & poststart = postend & instart = poststart) return root; int I; for (I = instart; I <= inend; ++ I) {If (inorder [I] = postorder [postend]) break; // locate the Middle Order Root Node} if (I> instart) Root-> left = buildtree (inorder, postorder, instart, I-1, poststart, poststart + (I-instart-1 )); if (I <inend) Root-> right = buildtree (inorder, postorder, I + 1, inend, poststart + I-instart, postend-1); Return root ;} treenode * buildtree (vector <int> & inorder, vector <int> & postorder) {int inlength = inorder. size (), postlength = postorder. size (); If (inlength = 0 | inleng Th! = Postlength) return NULL; return buildtree (inorder, postorder, 0, inlength-1, 0, postlength-1) ;}; class solution {public: treenode * buildtree (vector <int> & preorder, vector <int> & inorder, int prestart, int preend, int instart, int inend) {treenode * root = new treenode (preorder [prestart]); If (instart = inend & prestart = preend & instart = prestart) return root; int I; for (I = instart; I <= inend; ++ I ){ If (inorder [I] = preorder [prestart]) break; // locate the root node in the middle order} if (I> instart) Root-> left = buildtree (preorder, inorder, prestart + 1, prestart + I-instart, instart, I-1); if (I <inend) Root-> right = buildtree (preorder, inorder, prestart + I-instart + 1, preend, I + 1, inend); Return root;} treenode * buildtree (vector <int> & preorder, vector <int> & inorder) {int prelength = preorder. size (), inlength = inorder. Size (); If (inlength = 0 | inlength! = Prelength) return NULL; return buildtree (preorder, inorder, 0, prelength-1, 0, inlength-1 );}};