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LC106constructBinaryTreeFromInorderAndPostorderTraversal.cpp
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LC106constructBinaryTreeFromInorderAndPostorderTraversal.cpp
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struct TreeNode {
int val;
TreeNode *left;
TreeNode *right;
TreeNode() : val(0), left(nullptr), right(nullptr) {}
TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
TreeNode(int x, TreeNode *left, TreeNode *right)
: val(x), left(left), right(right) {}
};
#include <map>
#include <vector>
using namespace std;
class Solution {
public:
TreeNode *buildTree(vector<int> &inorder, vector<int> &postorder) {
map<int, int> M;
for (int i = 0; i < inorder.size(); i++) M[inorder[i]] = i;
return buildTreeWithRange(inorder, postorder, 0, inorder.size() - 1, 0,
postorder.size() - 1, M);
}
private:
static inline TreeNode *buildTreeWithRange(vector<int> &inorder,
vector<int> &postorder,
int inorderBegin, int inorderEnd,
int postorderBegin,
int postorderEnd,
map<int, int> &M) {
if (inorderEnd < inorderBegin || postorderEnd < postorderBegin)
return nullptr;
int rootValue = postorder[postorderEnd];
int rootIndinInorder = M[rootValue];
return new TreeNode(
rootValue,
buildTreeWithRange(
inorder, postorder, inorderBegin, rootIndinInorder - 1,
postorderBegin,
postorderBegin + rootIndinInorder - inorderBegin - 1, M),
buildTreeWithRange(inorder, postorder, rootIndinInorder + 1,
inorderEnd,
postorderEnd - inorderEnd + rootIndinInorder,
postorderEnd - 1, M));
}
};