func_code_string: #include <bits/stdc++.h>   const int inf = 0x7FFFFFFF;   using namespace std;   int dep[2014], shortcut[20][2014];   struct Edge {     int u, v, w;     bool operator<(const Edge &A) const { return w < A.w; }   } E[4000005];   int mp[2014][2014];   int fa[2014], d[2014];   int find(int x) { return x == fa[x] ? x : fa[x] = find(fa[x]); }   vector<int> G[2014], Q;   int get_lca(int a, int b) {     if (dep[a] < dep[b]) swap(a, b);     for (int i = 20 - 1; i >= 0; i--) {       if (dep[a] - dep[b] >> i & 1) {         a = shortcut[i][a];       }     }     if (a == b) return a;     for (int i = 20 - 1; i >= 0; i--) {       if (shortcut[i][a] != shortcut[i][b]) {         a = shortcut[i][a];         b = shortcut[i][b];       }     }     return shortcut[0][a];   }   int main() {     int N;     scanf( %d , &N);     for (int i = 1; i <= N; i++)       for (int j = 1; j <= N; j++) scanf( %d , &mp[i][j]);     int tot = 0;     for (int i = 1; i <= N; i++)       for (int j = i + 1; j <= N; j++) {         E[tot].u = i;         E[tot].v = j;         E[tot].w = mp[i][j];         tot++;       }     sort(E, E + tot);     for (int i = 1; i <= N; i++) fa[i] = i;     for (int i = 0; i < tot; i++) {       int u = E[i].u;       int v = E[i].v;       if (find(u) != find(v)) {         fa[find(u)] = find(v);         G[u].push_back(v);         G[u].push_back(E[i].w);         G[v].push_back(u);         G[v].push_back(E[i].w);       }     }     int *parent = shortcut[0];     d[1] = 0;     parent[1] = -1;     dep[1] = 0;     Q.push_back(1);     for (int head = 0; head < int(Q.size()); head++) {       int u = Q[head];       for (int i = 0; i < int(G[u].size()); i += 2) {         int v = G[u][i];         int w = G[u][i + 1];         if (v != parent[u]) {           parent[v] = u;           dep[v] = dep[u] + 1;           d[v] = d[u] + w;           Q.push_back(v);         }       }     }     for (int i = 1; i < 20; i++) {       for (int j = 1; j <= N; j++) {         int &res = shortcut[i][j];         res = shortcut[i - 1][j];         if (~res) {           res = shortcut[i - 1][res];         }       }     }     bool ok = true;     int num = 0;     for (int i = 1; i <= N; i++)       if (fa[i] == i) num++;     if (num > 1) ok = false;     for (int u = 1; ok && u <= N; u++) {       if (mp[u][u] != 0) ok = false;       for (int v = u + 1; ok && v <= N; v++) {         if (mp[u][v] != mp[v][u]) ok = false;         if (mp[u][v] == 0) ok = false;         int mid = get_lca(u, v);         if (d[u] + d[v] - d[mid] * 2 != mp[u][v]) ok = false;       }     }     puts(ok ?  YES  :  NO );     return 0;   }   