LC 572. Subtree of Another Tree

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<int> spre,tpre;

    bool isSubtree(TreeNode* s, TreeNode* t) {
        preorder(s,spre);
        preorder(t,tpre);

        vector<int> table(tpre.size());
        int len=0;
        for(int i=1;i<tpre.size();i++){
            if(tpre[i]==tpre[len]){
                len++;
                table[i]=len;
            }else{
                if(len==0) {
                    table[i]=0;
                }else{
                    len=table[len-1];
                    i--;
                }
            }
        }
        int i=0;
        int j=0;
        while(i<spre.size()){
            if(spre[i]==tpre[j]){
                i++;
                j++;
                if(j==tpre.size()) return true;
            }else{
                if(j==0){
                    i++;
                }else{
                    j=table[j-1];
                }
            }
        }
        return false;
    }

    void preorder(TreeNode* t, vector<int>& vs){
        if(t==nullptr) return;
        vs.push_back(t->val);
        if(t->left) preorder(t->left,vs);
        else vs.push_back(INT_MIN);
        if(t->right) preorder(t->right,vs);
        else vs.push_back(INT_MAX);
    }
};