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AtCoder - abc233_d

小_北_爸 2022-01-27 阅读 97

题意,给定n个数,m。求n个数中有多少连续的区间和等于m

题解:用前缀和优化,mp数组记录值,要开long long 不然wa

代码:

#include <bits/stdc++.h>
#define endl "\n"
#define rep(i, m, n) for (int i = (m); i <= (n); ++i)
#define rrep(i, m, n) for (int i = (m); i >= (n); --i)
#define IOS ios::sync_with_stdio(0); cin.tie(0);
#define mem(a,x) memset(a,x,sizeof(a))
using namespace std;
const int maxn = 2e5 + 10;
typedef long long ll;
map<ll,ll> mp;
ll m,a[maxn],s[maxn],n;
int main()
{
	IOS cin >> n >> m;
	rep(i,1,n){
		cin >> a[i]; s[i] = s[i-1] + a[i];
	}
	// 8 5 10 17 17 13
	ll ans = 0;
	mp[0] = 1;
	rep(r,1,n){ //枚举右端点 
		//如果满足s[r] - s[l-1] = m  ans加上从前的左端点个数 
		if(mp[s[r] - m]) ans += mp[s[r] - m];
		mp[s[r]]++; //记录左端点 
	}
	cout << ans << '\n';	
	return 0;
}
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