Pathwalks 線段樹動態開點優化DP
阿新 • • 發佈:2018-12-15
題意:
略。
題解:
每個點一個線段樹,來優化DP。
用線段樹動態開點。
然而這裡學到了一個技巧:用map陣列模擬二維陣列,達到動態開點的效果,然後用樹狀陣列求1-n最大值即可。
複雜度O(nlog^2n),也可以用unordered_map加速。
程式碼:
#include <bits/stdc++.h> #ifdef LOCAL #define debug(x) cout<<#x<<" = "<<(x)<<endl; #else #define debug(x) 1; #endif #define chmax(x,y) x=max(x,y) #define chmin(x,y) x=min(x,y) #define lson id<<1,l,mid #define rson id<<1|1,mid+1,r #define lowbit(x) x&-x #define mp make_pair #define pb push_back #define fir first #define sec second using namespace std; typedef long long ll; typedef unsigned long long ull; typedef pair<int, int> pii; const int MOD = 1e9 + 7; const double PI = acos (-1.); const double eps = 1e-10; const int INF = 0x3f3f3f3f; const ll INFLL = 0x3f3f3f3f3f3f3f3f; const int MAXN = 5e5 + 5; unordered_map<int, int> tree[MAXN]; int query (int x, int id) { int ret = 0; while (x) { ret = max(ret, tree[id][x]); x -= lowbit(x); } return ret; } void add (int x, int id, int v) { while (x <= 100001) { tree[id][x] = max(tree[id][x], v); x += lowbit(x); } } int main() { #ifdef LOCAL freopen ("input.txt", "r", stdin); #endif int n, m; int ans = 0; scanf ("%d %d", &n, &m); for (int i = 1; i <= m; i++) { int a, b, w; scanf ("%d %d %d", &a, &b, &w); w++; int ret = 0; ans = max(ans, ret = query(w - 1, a) + 1); add(w, b, ret); } printf ("%d\n", ans); return 0; }