技巧汇总

1. 修改set里面的非键值。

用mutable来修饰这个非键值。

举例代码：

#include<bits/stdc++.h>
using namespace std;
#define Fopen freopen("_in.txt","r",stdin); freopen("_out.txt","w",stdout);
#define LL long long
#define ULL unsigned LL
#define fi first
#define se second
#define pb push_back
#define lson l,m,rt<<1
#define rson m+1,r,rt<<1|1
#define lch(x) tr[x].son[0]
#define rch(x) tr[x].son[1]
#define max3(a,b,c) max(a,max(b,c))
#define min3(a,b,c) min(a,min(b,c))
typedef pair<int,int> pll;
const int inf = 0x3f3f3f3f;
const int _inf = 0xc0c0c0c0;
const LL INF = 0x3f3f3f3f3f3f3f3f;
const LL _INF = 0xc0c0c0c0c0c0c0c0;
const LL mod =  (int)1e9+7;
const int N = 2e5 + 100;
struct Node{
    int l;
    mutable int v;
    bool operator < (const Node & x) const{
        return l < x.l;
    }
    Node(int a, int b): l(a), v(b){};
};
set<Node> st;
int main(){
    st.insert(Node(1, 2));
    set<Node>::iterator it = st.lower_bound(Node(0, 0));
    cout << (*it).l << " " << (*it).v << endl;
    (*it).v = 3;
    cout << (*it).l << " " << (*it).v << endl;

    return 0;
}