decide if binary tree a contains binary tree b?

gistfile1.txt

#include <iostream>
using namespace std;

typedef struct _node {
    _node* left;
    _node* right;
    char c;
}node;


// it does not mean exactly match.
// it means that all b's nodes are equal with a's corresponding nodes.
bool tree_match(node *a, node* b) {
    if (b == NULL) {
        return true;
    }
    else if (a == NULL) {
        return false;
    }

    if (b->left == NULL && b->right == NULL && b->c == a->c) {
        return true;
    }
    
    if (a->c == b->c && tree_match(a->left, b->left) && tree_match(a->right, b->right)) {
        return true;
    }
    return false;
}
   
// go through all nodes.
bool contains(node* a, node*b) {
    if (tree_match(a, b)) {
        return true;
    }
    else if (tree_match(a->left, b) || tree_match(a->right, b)) {
        return true;
    }
    return false;
}

int main(int argc, char* argv[]) {
    node* a = new node;
    a->left = new node;
    a->right = new node;
    a->c = 'A';

    a->left->left = a->left->right = NULL;
    a->left->c = 'B';
    a->right->left = a->right->right = NULL;
    a->right->c = 'C';

    // a
    // /\
    // b c
    // /\/\
    // ####

    node* b = new node;
    b->c = 'B';
    b->left=b->right=NULL;
    // b
    // /\
    // # #
    if (contains(a,b)) {
        cout << "yes" << endl;
    }
    else {
        cout << "no" << endl;
    }
    return 0;
}