题目链接：https://vjudge.net/contest/332656#problem/E
思路：
稍微改下线段树求连续区间的代码就好了
具体的解释还是看代码注释吧
1 #include <math.h> 2 #include <stdio.h> 3 #include <stdlib.h> 4 #include <iostream> 5 #include <algorithm> 6 #include <string> 7 #include <string.h> 8 #include <vector> 9 #include <map> 10 #include <stack> 11 #include <set> 12 #include <random> 13 14 #define LL long long 15 #define ls nod<<1 16 #define rs (nod<<1)+1 17 const int maxn = 2e5 + 10; 18 const double eps = 1e-9; 19 20 21 LL v[maxn]; 22 struct Node { 23 int l,r; 24 int lsum,rsum,sum; 25 }tree[maxn<<2]; 26 27 void build(int l,int r,int nod) { 28 tree[nod].l = l; 29 tree[nod].r = r; 30 tree[nod].lsum = tree[nod].rsum = tree[nod].sum = r-l+1; 31 if (l == r ) { 32 return ; 33 } 34 int mid = (l + r) >> 1; 35 build(l,mid,nod<<1); 36 build(mid+1,r,(nod<<1)+1); 37 } 38 39 void pushup(int nod) { 40 int l = tree[nod].l,r = tree[nod].r; 41 int mid = (l + r ) >> 1; 42 tree[nod].sum = std::max(std::max(tree[ls].sum,tree[rs].sum),tree[ls].rsum + tree[rs].lsum); 43 tree[nod].lsum = tree[ls].lsum; 44 tree[nod].rsum = tree[rs].rsum; 45 if (mid - l + 1 == tree[ls].lsum) 46 tree[nod].lsum = tree[ls].sum + tree[rs].lsum; 47 if (r-mid == tree[rs].rsum) 48 tree[nod].rsum = tree[rs].sum + tree[ls].rsum; 49 } 50 51 52 void modify(int x,int z,int nod=1) { 53 int l = tree[nod].l,r = tree[nod].r; 54 if (l == r) { 55 tree[nod].sum = tree[nod].lsum = tree[nod].rsum = z; 56 return ; 57 } 58 int mid = (l + r) >> 1; 59 if (x <= mid) { 60 modify(x,z,nod<<1); 61 } 62 if (x > mid) { 63 modify(x,z,(nod<<1)+1); 64 } 65 pushup(nod); 66 } 67 68 LL query(int x,int nod=1) { 69 int l = tree[nod].l,r = tree[nod].r; 70 if(l == r) 71 return tree[nod].sum; 72 int mid = (l + r) >> 1; 73 if (x <= mid) { 74 if (x >= tree[ls].r - tree[ls].rsum + 1) { 75 return tree[ls].rsum + tree[rs].lsum; 76 } 77 else { 78 return query(x,ls); 79 } 80 } 81 else { 82 if (x <= tree[rs].lsum + tree[rs].l - 1) { 83 return tree[ls].rsum + tree[rs].lsum; 84 } 85 else 86 return query(x,rs); 87 } 88 } 89 90 int main() { 91 int n,m,x; 92 char s[2]; 93 while (~scanf("%d%d",&n,&m)) { 94 std::stack<int> sta; 95 build(1,n,1); 96 while (m--) { 97 scanf("%s",s); 98 if (s[0] == 'D') { 99 scanf("%d",&x); 100 modify(x,0); 101 sta.push(x); 102 } 103 else if (s[0] == 'R') { 104 x = sta.top(); 105 sta.pop(); 106 if (x > 0) 107 modify(x,1); 108 } 109 else { 110 scanf("%d",&x); 111 printf("%lld ",query(x)); 112 } 113 } 114 } 115 return 0; 116 }