diff --git a/segtree.cpp b/segtree.cpp
new file mode 100644
index 0000000..38b4af0
--- /dev/null
+++ b/segtree.cpp
@@ -0,0 +1,116 @@
+#include <bits/stdc++.h>
+using namespace std;
+class Solution {
+public:
+    struct tnode{
+        int l,r;
+        int sum;//segment sum
+        int val;//segment max
+    };
+    //vector<int> a;//input
+    vector<struct tnode> tree;
+    void buildtree(int no,int l,int r,vector<int> &a){
+        tree[no].l=l;
+        tree[no].r=r;
+        int mid=(l+r)/2;
+        if (l==r){
+            //segment max
+            tree[no].val=a[l];
+            //segment sum
+            //tree[no].sum=a[l];
+        }
+        else{
+            buildtree(no*2,l,mid,a);
+            buildtree(no*2+1,mid+1,r,a);
+            // segment max
+            tree[no].val=max(tree[no*2].val,tree[no*2+1].val);
+            // segment sum
+            //tree[no].sum=tree[no*2].sum+tree[no*2+1].sum;
+        }
+        return;
+    }
+    /*
+    //更新区间和
+    void update0(int no,int lr, int val) {
+        if (tree[no].l==lr && tree[no].r==lr){
+            tree[no].sum=val;
+            return;
+        }
+
+        int mid=(tree[no].l+tree[no].r)/2;
+        if (lr>mid){
+            update0(no*2+1,lr,val);
+        }
+        else{
+            update0(no*2,lr,val);
+        }
+        tree[no].sum=tree[no*2].sum+tree[no*2+1].sum;
+    }
+
+    void update(int index, int val) {
+        update0(1,index+1,val);
+    }
+
+    //查找区间和
+    int query(int no,int l, int r) {
+        if (tree[no].l==l && tree[no].r==r)
+            return tree[no].sum;
+
+        int mid=(tree[no].l+tree[no].r)/2;
+        if (l>mid)
+            return query(no*2+1,l,r);
+        else if (r<=mid)
+            return query(no*2,l,r);
+        else
+            return query(no*2,l,mid)+query(no*2+1,mid+1,r);
+    }
+    */
+    //查找区间大于v的最左侧位置
+    int query(int no,int v, int pos,int l, int r) {
+        if (tree[no].val<=v)
+            return -1;
+        if (l==r)
+            return l;
+
+        int mid=(l+r)/2;
+        if (pos<=mid){
+            int res=query(no*2,v,pos,l,mid);
+            if (res>=0)
+                return res;
+        }
+        return query(no*2+1,v,pos,mid+1,r);
+    }
+
+    vector<int> leftmostBuildingQueries(vector<int>& heights, vector<vector<int>>& queries) {
+        int n=heights.size();
+        tree.resize(4*n+1);
+        buildtree(1,0,n-1,heights);
+        int qn=queries.size();
+        vector<int> res(qn);
+        for (int i=0;i<qn;i++){
+            int a=queries[i][0];
+            int b=queries[i][1];
+            if (a>b) swap(a,b);
+            if (a==b){
+                res[i]=a;
+            }else if (heights[b]>heights[a]){
+                res[i]=b;
+            }else{
+                res[i]=query(1,heights[a],b+1,0,n-1);
+            }
+        }
+        return res;
+    }
+};
+int main()
+{
+    Solution sol;
+    vector<int> heights={3,1,2,4,5};
+    vector<vector<int>> queries={{0,1},{1,0}};
+    vector<int> res=sol.leftmostBuildingQueries(heights,queries);
+    for (auto r:res){
+        cout << r << " ";
+    }
+    cout << endl;
+    return 0;
+}