diff --git a/OnlineJudges/lydsy/1196.cpp b/OnlineJudges/lydsy/1196.cpp
new file mode 100644
index 0000000..18c913f
--- /dev/null
+++ b/OnlineJudges/lydsy/1196.cpp
@@ -0,0 +1,26 @@
+#include <cstdio>
+#include <cstring>
+int fa[10010], X[20010], Y[20010], C1[20010], C2[20010], n, k, m;
+int Find(int x) { return fa[x] == -1 ? x : fa[x] = Find(fa[x]); }
+bool check(int x)
+{
+    memset(fa, -1, sizeof(fa));
+    int cnt1 = 0, cnt2 = 0;
+    for (int i = 1, fx, fy; i < m; i++)
+        if ((C1[i] <= x) && ((fx = Find(X[i])) != (fy = Find(Y[i]))))
+            cnt1++, fa[fx] = fy;
+    for (int i = 1, fx, fy; i < m; i++)
+        if ((C2[i] <= x) && ((fx = Find(X[i])) != (fy = Find(Y[i]))))
+            cnt2++, fa[fx] = fy;
+    return cnt1 >= k && cnt1 + cnt2 == n - 1;
+}
+int main()
+{
+    scanf("%d%d%d", &n, &k, &m);
+    for (int i = 1; i < m; i++)
+        scanf("%d%d%d%d", X + i, Y + i, C1 + i, C2 + i);
+    int l = 0, r = 0x3f3f3f3f, mid;
+    while (l < r) check(mid = (l + r) >> 1) ? r = mid : l = mid + 1;
+    printf("%d", l);
+    return 0;
+}
\ No newline at end of file
diff --git a/OnlineJudges/lydsy/1821.cpp b/OnlineJudges/lydsy/1821.cpp
new file mode 100644
index 0000000..66f2313
--- /dev/null
+++ b/OnlineJudges/lydsy/1821.cpp
@@ -0,0 +1,35 @@
+#include <algorithm>
+#include <cmath>
+#include <cstdio>
+#include <cstring>
+using namespace std;
+int n, k, fa[1010], X[1010], Y[1010], cnt, ecnt;
+double ans;
+int Find(int x) { return fa[x] == -1 ? x : fa[x] = Find(fa[x]); }
+struct edge
+{
+    int u, v;
+    double l;
+    bool operator<(const edge &rhs) const { return l < rhs.l; }
+}edges[1000010];
+int main()
+{
+    memset(fa, -1, sizeof(fa));
+    scanf("%d%d", &n, &k);
+    for (int i = 1; i <= n; i++) scanf("%d%d", X + i, Y + i);
+    for (int i = 1; i <= n; i++)
+        for (int j = 1; j < i; j++, ecnt++)
+            edges[ecnt].u = i, edges[ecnt].v = j,
+            edges[ecnt].l = sqrt((X[i] - X[j]) * (X[i] - X[j]) +
+            (Y[i] - Y[j]) * (Y[i] - Y[j]));
+    sort(edges, edges + ecnt);
+    for (int i = 0, fx, fy; i < ecnt; i++)
+        if ((fx = Find(edges[i].u)) != (fy = Find(edges[i].v)))
+        {
+            fa[fx] = fy;
+            cnt++, ans = edges[i].l;
+            if (cnt - 1 == n - k) break;
+        }
+    printf("%.2lf", ans);
+    return 0;
+}
\ No newline at end of file
diff --git a/OnlineJudges/lydsy/4152.cpp b/OnlineJudges/lydsy/4152.cpp
new file mode 100644
index 0000000..3e16778
--- /dev/null
+++ b/OnlineJudges/lydsy/4152.cpp
@@ -0,0 +1,62 @@
+#include <algorithm>
+#include <cctype>
+#include <cstdio>
+#include <cstring>
+#include <queue>
+using namespace std;
+const int maxn = 200010;
+inline void readInt(int &x)
+{
+    int ch = x = 0;
+    while (!isdigit(ch = getchar()));
+    for (; isdigit(ch); ch = getchar()) x = x * 10 + ch - '0';
+}
+int head[maxn], to[maxn << 2], nxt[maxn << 2], len[maxn << 2], ecnt, n;
+inline void addEdge(int f, int t, int l)
+{
+    ecnt++;
+    nxt[ecnt] = head[f];
+    head[f] = ecnt;
+    to[ecnt] = t;
+    len[ecnt] = l;
+}
+struct P { int id, x, y; } ps[maxn];
+bool cmpx(const P &lhs, const P &rhs) { return lhs.x < rhs.x; }
+bool cmpy(const P &lhs, const P &rhs) { return lhs.y < rhs.y; }
+int pathlen[maxn];
+struct heapnode
+{
+    int id, dis;
+    heapnode(int x, int y) :id(x), dis(y) {}
+    bool operator<(const heapnode &rhs) const { return dis > rhs.dis; }
+};
+int main()
+{
+    readInt(n);
+    for (int i = 0; i < n; i++) ps[i].id = i + 1, readInt(ps[i].x), readInt(ps[i].y);
+    sort(ps, ps + n, cmpx);
+    for (int i = 0; i < n - 1; i++)
+        addEdge(ps[i].id, ps[i + 1].id, ps[i + 1].x - ps[i].x),
+        addEdge(ps[i + 1].id, ps[i].id, ps[i + 1].x - ps[i].x);
+    sort(ps, ps + n, cmpy);
+    for (int i = 0; i < n - 1; i++)
+        addEdge(ps[i].id, ps[i + 1].id, ps[i + 1].y - ps[i].y),
+        addEdge(ps[i + 1].id, ps[i].id, ps[i + 1].y - ps[i].y);
+    memset(pathlen, 0x3f3f3f3f, sizeof(pathlen));
+    pathlen[1] = 0;
+    priority_queue<heapnode> Q;
+    Q.push(heapnode(1, 0));
+    while (!Q.empty())
+    {
+        heapnode x = Q.top(); Q.pop();
+        if (x.dis > pathlen[x.id]) continue;
+        for (int cur = head[x.id]; cur; cur = nxt[cur])
+            if (pathlen[to[cur]] > pathlen[x.id] + len[cur])
+            {
+                pathlen[to[cur]] = pathlen[x.id] + len[cur];
+                Q.push(heapnode(to[cur], pathlen[to[cur]]));
+            }
+    }
+    printf("%d", pathlen[n]);
+    return 0;
+}
\ No newline at end of file