Codeforces 272C Dima and Staircase 思维 or 线段树

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题意:给出n个物品高度ai,ai<=1e9,ai非递减,n,m<=1e5,m个方块的宽度和高度,问m个方块依次落下时达到的高度

每次都从左端点1开始叠放,第i个方块肯定落在第i-1个方块的上方 取高度边界low=ans[i-1]+h[i-1]
高度递增,(下标>=i)高度>=a[i]的都能放的宽度为i的方块
若l<a[w] ans[i]=a[w] 
若l>=a[w] ans[i]=l (因为高度l以上的宽度都大于等于w) 

#include <bits/stdc++.h>using namespace std;typedef long long ll;const int N=2e5+20;ll n,m,a[N],w[N],h[N];ll ans[N];int main(){while(cin>>n){ll mx=0;for(int i=1;i<=n;i++){scanf("%I64d",&a[i]);mx=max(mx,a[i]);}cin>>m;for(int i=1;i<=m;i++)scanf("%I64d%I64d",&w[i],&h[i]);ans[0]=h[0]=0;for(int i=1;i<=m;i++){ll l=ans[i-1]+h[i-1];if(w[i]>n||l>=mx)//防止a[w[i]]溢出 w[i]<=1e9 ans[i]=l;else if(l<a[w[i]])ans[i]=a[w[i]];elseans[i]=l;cout<<ans[i]<<endl;}}return 0;} 

线段树做法(转载)

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对于每一个箱子，只需要查询[1,Wi]内的最大值，箱子会被这个最大值支撑着，所以输出这个最大值，放上这个箱子之后，这个区间内的所有值都会变成上述的那个最大值加上箱子的高度Hi。用线段树维护即可。

#include<cstdio>#include<cstring>#include<algorithm>#define LL long long#define maxn 100005using namespace std;struct node{int l, r;LL c, maxh;}tree[maxn << 2];int h[maxn];void pushdown(int id){if (tree[id].c){tree[id << 1].c = tree[id].c;tree[id << 1 | 1].c = tree[id].c;tree[id << 1].maxh = tree[id].maxh;tree[id << 1 | 1].maxh = tree[id].maxh;}}void build(int id, int l, int r){tree[id].l = l;tree[id].r = r;if (tree[id].l == tree[id].r){tree[id].maxh = h[l];}else{int mid = (tree[id].l + tree[id].r) >> 1;build(id << 1, l, mid);build(id << 1 | 1, mid + 1, r);tree[id].maxh = max(tree[id << 1].maxh, tree[id << 1 | 1].maxh);}}void op(int id, int l, int r, LL c){if (l <= tree[id].l&&tree[id].r <= r){tree[id].c = c;tree[id].maxh = c;}else{pushdown(id);int mid = (tree[id].l + tree[id].r) >> 1;if (l <= mid) op(id << 1, l, r, c);if (mid<r) op(id << 1 | 1, l, r, c);tree[id].maxh = max(tree[id << 1].maxh, tree[id << 1 | 1].maxh);}}LL que(int id, int l, int r){if (l <= tree[id].l&&tree[id].r <= r){return tree[id].maxh;}else{pushdown(id);int mid = (tree[id].l + tree[id].r) >> 1;LL res = 0;if (l <= mid) res = max(res, que(id << 1, l, r));if (mid<r) res = max(res, que(id << 1 | 1, l, r));return res;}}int main(){int n;scanf("%d", &n);for (int i = 1; i <= n; i++) scanf("%d", &h[i]);int m;scanf("%d", &m);build(1, 1, n);while (m--){LL w, h;scanf("%I64d %I64d", &w, &h);LL tmp = que(1, 1, w);printf("%I64d\n", tmp);op(1, 1, w, tmp + h);}return 0;}