PAT 1043 Is It a Binary Search Tree

#include <cstdio>

#include <climits>

#include <cstdlib>

#include <vector>



const double LO_BOUND = -1.0 + INT_MIN;

const double HI_BOUND = +1.0 + INT_MAX;



using namespace std;



class Node {

public:

    Node* L;

    Node* R;

    int data;

    Node(int d=0, Node* l = NULL, Node* r = NULL) : L(l), R(r), data(d){}

};





Node* build_bst(vector<Node> &nums, int start, int end, bool mirror = false) {

    if (start >= end) return NULL;

    if (start + 1 == end) {

        nums[start].R = nums[start].L = NULL;

        return &nums[start];

    }

    Node& root = nums[start];

    int i = start + 1;

    while (i<end) {

        if (!mirror) {

            if (nums[i].data >= root.data) break;

        } else {

            if (nums[i].data < root.data) break;

        }

        i++;

    }

//    printf("Root: %d\n", start);

//    printf("L: %d-%d\n", start + 1, i);

//    printf("R: %d-%d\n", i, end);

    

    root.L = build_bst(nums, start + 1, i, mirror);

    root.R = build_bst(nums, i, end, mirror);

    

    return &root;

}



bool is_bst(Node* root, bool mirror = false, double lo = LO_BOUND, double hi = HI_BOUND) {

    if (root == NULL) return true;

//    printf("check %d lo=%f hi=%f mirror=%d\n", root->data, lo, hi, mirror);

    if (root->data < lo || root->data >= hi) {

//        printf("fail\n");

        return false;

    }

    Node *vL = root->L, *vR = root->R, *tmp = NULL;

    if (mirror) {

        tmp = vL;

        vL = vR;

        vR = tmp;

    }

    return is_bst(vL, mirror, lo, root->data) && is_bst(vR, mirror, root->data, hi);

}



void postorder(Node* root, vector<int> &v) {

    if (root == NULL) return;

    postorder(root->L, v);

    postorder(root->R, v);

    v.push_back(root->data);

    return;

}



void print(vector<int> &v) {

    int len = v.size();

    

    if (len < 1) return;

    printf("%d", v[0]);

    for (int i=1; i<len; i++) {

        printf(" %d", v[i]);

    }

    printf("\n");

}

int main() {

    int N;

    scanf("%d", &N);

    vector<Node> nums(N);

    

    for (int i=0; i<N; i++) {

        scanf("%d", &(nums[i].data));

    }

    vector<int> post;

    

    Node* root = build_bst(nums, 0, nums.size());

    if (is_bst(root)) {

        printf("YES\n");

        postorder(root, post);

        print(post);

        return 0;

    }



    root = build_bst(nums, 0, nums.size(), true);

    if (is_bst(root, true)) {

        printf("YES\n");

        postorder(root, post);

        print(post);

        return 0;

    } else {

        printf("NO\n");

    }

    return 0;

}

就这样吧，还有那么多题拙计啊