func_code_string: #include <bits/stdc++.h>   using namespace std;   template <class T>   struct node {     T val;     T lazy;     int l, r;     node* left;     node* right;     node(int l, int r) {       this->l = l;       this->r = r;       this->left = nullptr;       this->right = nullptr;     }   };   template <class T, int SZ>   struct segtree {     T combIdentity = -1e9;     T comb(T l, T r) { return max(l, r); }     T pushIdentity = 0;     void push(node<T>* n) {       n->val += n->lazy;       if (n->l != n->r) {         n->left->lazy += n->lazy;         n->right->lazy += n->lazy;       }       n->lazy = pushIdentity;     }     node<T>* root;     segtree() {       int ub = 1;       while (ub < SZ) ub *= 2;       root = new node<T>(0, ub - 1);       root->val = pushIdentity;       root->lazy = pushIdentity;     }     void propagate(node<T>* n) {       if (n->l != n->r) {         int mid = ((n->l) + (n->r)) / 2;         if (n->left == nullptr) {           n->left = new node<T>(n->l, mid);           n->left->val = pushIdentity;           n->left->lazy = pushIdentity;         }         if (n->right == nullptr) {           n->right = new node<T>(mid + 1, n->r);           n->right->val = pushIdentity;           n->right->lazy = pushIdentity;         }       }       push(n);     }     void updN(node<T>* n, int i1, int i2, T val) {       propagate(n);       if (i2 < n->l || i1 > n->r) return;       if (i1 <= n->l && i2 >= n->r) {         n->lazy = val;         push(n);         return;       }       updN(n->left, i1, i2, val);       updN(n->right, i1, i2, val);       n->val = comb(n->left->val, n->right->val);     }     void upd(int i1, int i2, T val) { updN(root, i1, i2, val); }     T queryN(node<T>* n, int i1, int i2) {       propagate(n);       if (i2 < n->l || i1 > n->r) return combIdentity;       if (n->l >= i1 && n->r <= i2) return n->val;       T a = combIdentity;       if (n->left != nullptr) a = comb(a, queryN(n->left, i1, i2));       if (n->right != nullptr) a = comb(a, queryN(n->right, i1, i2));       return a;     }     T query(int i1, int i2) { return queryN(root, i1, i2); }   };   const int MAX_M = 20020;   const int MAX_N = 52;   int n, m, k;   int arr[MAX_N][MAX_M];   int pref[MAX_N][MAX_M];   int dp[MAX_N][MAX_M];   int getsum(int i, int j) {     if (j == 0)       return pref[i][j + k - 1];     else {       return pref[i][j + k - 1] - pref[i][j - 1];     }   }   int get(int i, int j) { return getsum(i, j) + getsum(i + 1, j); }   pair<int, int> getBounds(int j) {     int l = j - k + 1;     int r = j;     l = max(0, l);     r = min(m - k, r);     return make_pair(l, r);   }   int main() {     ios::sync_with_stdio(0);     cin.tie(0);     cin >> n >> m >> k;     for (int i = 0; i < n; i++)       for (int j = 0; j < m; j++) cin >> arr[i][j];     for (int i = 0; i < n; i++) {       pref[i][0] = arr[i][0];       for (int j = 1; j < m; j++) pref[i][j] = pref[i][j - 1] + arr[i][j];     }     for (int i = 0; i < m - k + 1; i++) dp[0][i] = get(0, i);     for (int i = 1; i < n; i++) {       segtree<int, MAX_M> st;       for (int j = 0; j < m - k + 1; j++) st.upd(j, j, dp[i - 1][j]);       for (int j = 0; j < k; j++) {         pair<int, int> b = getBounds(j);         st.upd(b.first, b.second, -arr[i][j]);       }       for (int j = 0; j < m - k + 1; j++) {         dp[i][j] = st.query(0, m - k) + get(i, j);         pair<int, int> b = getBounds(j);         st.upd(b.first, b.second, arr[i][j]);         b = getBounds(j + k);         st.upd(b.first, b.second, -arr[i][j + k]);       }     }     int res = 0;     for (int i = 0; i < m - k + 1; i++) res = max(res, dp[n - 1][i]);     return cout << res <<   n , 0;     ;   }   