TreeNode數據結構
struct TreeNode {
int val;
TreeNode * left;
TreeNode * right;
TreeNode(const int & _val = int(), TreeNode * _left = nullptr, TreeNode * _right = nullptr)
: val(_val), left(_left), right(_right) {}
};
遞歸
void preOrder(TreeNode * root) {
if (nullptr == root) {
return;
}
cout << root->val << ' ';
preOrder(root->left);
preOrder(root->right);
}
void inOrder(TreeNode * root) {
if (nullptr == root) {
return;
}
preOrder(root->left);
cout << root->val << ' ';
preOrder(root->right);
}
void postOrder(TreeNode * root) {
if (nullptr == root) {
return;
}
preOrder(root->left);
preOrder(root->right);
cout << root->val << ' ';
}
非遞歸方法(兩種)
const int capacity = 1 << 16;
void preOrder(TreeNode * root) {
TreeNode * stk[capacity];
TreeNode * tmp = root;
int top = 0;
while (tmp || top) {
while (tmp) {
cout << tmp->val << ' ';
stk[top++] = tmp;
tmp = tmp->left;
}
if (top) {
tmp = stk[--top];
tmp = tmp->right;
}
}
}
void inOrder(TreeNode * root) {
TreeNode * stk[capacity];
TreeNode * tmp = root;
int top = 0;
while (tmp || top) {
while (tmp) {
stk[top++] = tmp;
tmp = tmp->left;
}
if (top) {
tmp = stk[--top];
cout << tmp->val << ' ';
tmp = tmp->right;
}
}
}
void postOrder(TreeNode * root) {
TreeNode * stk[capacity];
TreeNode * tmp = root;
int top = 0;
stk[top++] = tmp;
stk[top++] = tmp;
while (top) {
tmp = stk[--top];
if (top && tmp == stk[top - 1]) {
if (tmp->right) {
stk[top++] = tmp->right;
stk[top++] = tmp->right;
}
if (tmp->left) {
stk[top++] = tmp->left;
stk[top++] = tmp->left;
}
}
else {
cout << tmp->val << ' ';
}
}
}
#define pitpb pair<TreeNode*, bool>
const int capacity = 1 << 16;
void preOrder(TreeNode * root) {
pitpb stk[capacity];
int top = 0;
stk[top++] = pitpb(root, false);
while (top) {
pitpb tmp = stk[--top];
if (!tmp.first) {
continue;
}
if (tmp.second) {
cout << tmp.first->val << ' ';
}
else {
stk[top++] = pitpb(tmp.first->right, false);
stk[top++] = pitpb(tmp.first->left, false);
stk[top++] = pitpb(tmp.first, true);
}
}
}
void inOrder(TreeNode * root) {
pitpb stk[capacity];
int top = 0;
stk[top++] = pitpb(root, false);
while (top) {
pitpb tmp = stk[--top];
if (!tmp.first) {
continue;
}
if (tmp.second) {
cout << tmp.first->val << ' ';
}
else {
stk[top++] = pitpb(tmp.first->right, false);
stk[top++] = pitpb(tmp.first, true);
stk[top++] = pitpb(tmp.first->left, false);
}
}
}
void postOrder(TreeNode * root) {
pitpb stk[capacity];
int top = 0;
stk[top++] = pitpb(root, false);
while (top) {
pitpb tmp = stk[--top];
if (!tmp.first) {
continue;
}
if (tmp.second) {
cout << tmp.first->val << ' ';
}
else {
stk[top++] = pitpb(tmp.first, true);
stk[top++] = pitpb(tmp.first->right, false);
stk[top++] = pitpb(tmp.first->left, false);
}
}
}