leetcode 重建二叉樹
阿新 • • 發佈:2019-01-05
public TreeNode buildTree(int[] preorder, int[] inorder) {
int size = preorder.length;
if(size == 0)
return null;
return help(preorder, inorder, 0, size - 1, 0, size - 1);
}
public TreeNode help(int[] preorder, int[] inorder, int pleft, int pright, int ileft, int iright) {
if(pleft > pright || ileft > iright)
return null;
TreeNode root = new TreeNode(preorder[pleft]);
int i;
for(i = ileft; i <= iright; i++){
if(inorder[i] == preorder[pleft])
break;
}
root.left = help(preorder, inorder,pleft + 1 , pleft + i - ileft, ileft, i - 1);
root.right = help(preorder, inorder,pleft + i - ileft + 1, pright, i + 1, iright);
return root;
}
public TreeNode buildTree(int[] inorder, int[] postorder) {
int size = inorder.length;
if(size == 0)
return null ;
return help(inorder, postorder, 0, size - 1, 0, size - 1);
}
public TreeNode help(int[] inorder, int[] postorder, int ileft, int iright, int pleft, int pright) {
if(pleft > pright || ileft > iright)
return null;
TreeNode root = new TreeNode(postorder[pright]);
int i;
for(i = ileft; i <= iright; i++){
if(inorder[i] == postorder[pright])
break;
}
root.left = help(inorder, postorder,ileft, i - 1, pleft, pleft + i - ileft - 1);
root.right = help(inorder, postorder,i + 1, iright, pleft + i - ileft, pright - 1);
return root;
}