update

src/P3957/P3957.cpp

@@ -9,7 +9,8 @@ using ll = long long;
 auto &is = std::cin;
 auto &os = std::cout;
 
-const ll max_n = 5e5+5, ll_min{std::numeric_limits<decltype(ll_min)>::min()};
+const ll max_n = 5e5+5, ll_min{std::numeric_limits<decltype(ll_min)>::min()}, 
+                ll_max{std::numeric_limits<decltype(ll_max)>::max()};
 ll n, d, k;
 struct Point{
     ll posit,score;
@@ -21,33 +22,47 @@ void flush_exit(){
     _Exit(0);
 }
 
+bool check(const ll coin){
+    for(ll i{0};i<max_n;i++)dp[i]=ll_min;
+    dp[0]=0; // 注意第0个点是能到达的reachable
+    const ll max_step {coin+d}, min_step {std::max((ll)1,d-coin)};
+    for(ll i{1};i<=n;++i){
+        for(ll from{i-1};from>=0;from--){
+            ll dis{points[i].posit-points[from].posit};
+            if(min_step<=dis){
+                if(dis<=max_step){
+                    if(dp[from]==ll_min)continue;
+                    dp[i] = std::max(dp[i],dp[from]+points[i].score);
+                    if(dp[i]>=k){
+                        return true;
+                    }
+                }else{
+                    break;
+                }
+            }
+        }
+    }
+    return false;
+}
+
 int main(){
     is>>n>>d>>k;
     for(ll i{1};i<=n;++i){
         is>>points[i].posit>>points[i].score;
     }
-
-    for(ll coin{0};coin<=(points[n].posit-d);++coin){
-        for(ll i{0};i<max_n;i++)dp[i]=ll_min;
-        dp[0]=0; // 注意第0个点是能到达的reachable
-        const ll max_step {coin+d}, min_step {std::max((ll)1,d-coin)};
-        for(ll i{1};i<=n;++i){
-            for(ll from{i-1};from>=0;from--){
-                ll dis{points[i].posit-points[from].posit};
-                if(min_step<=dis){
-                    if(dis<=max_step){
-                        if(dp[from]==ll_min)continue;
-                        dp[i] = std::max(dp[i],dp[from]+points[i].score);
-                        if(dp[i]>=k){
-                            os<<coin<<'\n';
-                            flush_exit();
-                        }
-                    }else{
-                        break;
-                    }
-                }
-            }
+    
+    const ll max_coin{points[n].posit-d};//d+g = x[n] -> g = x[n]-d
+    ll l{0},r{max_coin},ans{ll_max};
+    while(l<=r){
+        ll mid{(l+r)/2};
+        const bool check_ret{check(mid)};
+        if(check_ret){
+            ans = mid;
+            r=mid-1;
+        }else{
+            l=mid+1;
         }
     }
-    os<<-1<<'\n';
+
+    os<<(ans==ll_max?-1:ans)<<'\n';
 }