Leetcode: Construct Binary Tree from Preorder and Inorder Traversal, Construct Binary Tree from Inorder and Postorder Traversal
总结:
1. 第 36 行代码, 最好是按照 len 来遍历, 而不是下标
代码: 前序中序
#include <iostream>
#include <vector>
using namespace std; struct TreeNode {
int val;
TreeNode *left;
TreeNode *right;
TreeNode(int x) : val(x), left(NULL), right(NULL) {}
}; class Solution {
public:
vector<int> preorder, inorder;
TreeNode *buildTree(vector<int> &preorder, vector<int> &inorder) {
TreeNode * root = NULL;
if(preorder.size() == 0 || inorder.size() == 0)
return root; this->preorder = preorder;
this->inorder = inorder;
for(int i = 0; i < inorder.size(); i ++) {
if(inorder[i] == preorder[0]) {
root = new TreeNode(preorder[0]);
int len1 = i;
int len2 = inorder.size()-i-1;
root->left = buildParty(1,0, len1);
root->right = buildParty(len1+1, i+1, len2);
return root;
}
}
}
TreeNode *buildParty(const int &p, const int &i, const int &len) {
if(len <= 0)
return NULL;
for(int cursor = 0; cursor < len; cursor++) {
int pos = cursor+i; if(inorder[pos] == preorder[p]) {
TreeNode *root = new TreeNode(preorder[p]);
int len1 = cursor;
int len2 = len-cursor-1;
root->left = buildParty(p+1, i, len1);
root->right = buildParty(p+len1+1, pos+1, len2);
return root;
}
}
}
}; int main() {
TreeNode *node; int in1[10] = {1, 2, 3, 4, 5, 6};
int in2[10] = {3, 2, 4, 1, 5, 6}; Solution solution;
node = solution.buildTree(vector<int>(in1, in1+6), vector<int>(in2, in2+6));
return 0;
}
代码: 中序后序
#include <iostream>
#include <vector>
using namespace std; struct TreeNode {
int val;
TreeNode *left;
TreeNode *right;
TreeNode(int x) : val(x), left(NULL), right(NULL) {}
}; class Solution {
public:
vector<int> inorder;
vector<int> postorder;
TreeNode *buildTree(vector<int> &inorder, vector<int> &postorder) {
TreeNode *root = NULL;
if(!inorder.size())
return root; this->inorder = inorder;
this->postorder = postorder; for(int ci = 0; ci < inorder.size(); ci++) {
if(inorder[ci] == postorder[postorder.size()-1]) {
root = new TreeNode(inorder[ci]);
int len1 = ci;
int len2 = inorder.size()-ci-1;
root->left = buildParty(0, postorder.size()-len2-2, len1);
root->right = buildParty(ci+1, postorder.size()-2, len2);
return root;
} }
}
TreeNode *buildParty(const int &i, const int &j, const int &len) {
if(!len)
return NULL; for(int ci = 0; ci < len; ci ++) {
int pos = i+ci;
if(postorder[j] == inorder[pos]) {
TreeNode *root = new TreeNode(inorder[pos]);
int len1 = ci;
int len2 = len-ci-1;
root->left = buildParty(i, j-len2-1, len1);
root->right = buildParty(i+ci+1, j-1, len2);
return root;
}
}
}
}; int main() {
TreeNode *node; int in1[10] = {3, 2, 4, 1, 5, 6};
int in2[10] = {3, 4, 2, 6, 5, 1}; Solution solution;
node = solution.buildTree(vector<int>(in1, in1+6), vector<int>(in2, in2+6));
return 0;
}
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