This submission is migrated from previous version of oj.uz, which used different machine for grading. This submission may have different result if resubmitted.
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<ll, ll> llp;
typedef pair<int, int> ii;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ii> vii;
typedef vector<vii> vvii;
#define pb(x) push_back(x)
#define mp(x, y) make_pair(x, y)
#define MOD ((ll)1e9+7)
#define safeadd(x, y) ( ( ((ll)x % MOD) + ((ll)y % MOD) ) % MOD )
#include <unordered_map>
int N;
unordered_map<int, ll> dp[500];
int A[500], B[500];
ll func(int x, int s) {
//cerr << "called: " << x << " " << s << endl;
if (dp[x][s] != 0) return dp[x][s];
ll sum = 0;
if (x < N-1) sum = safeadd(sum, func(x+1, s));
else sum = safeadd(sum, 1);
for (int i = max(s+1, A[x]); i <= B[x]; i++) {
if (x < N-1) sum = safeadd(sum, func(x+1, i));
else sum = safeadd(sum, 1);
}
dp[x][s] = sum;
//cerr << "returned: " << sum << endl;
return dp[x][s];
}
int main(int argc, char **argv) {
//freopen("input", "r", stdin);
//freopen("output", "w", stdout);
scanf("%d", &N);
for (int i = 0; i < N; i++) {
scanf("%d%d", &(A[i]), &(B[i]));
}
printf("%lld\n", safeadd(func(0, 0), -1));
return 0;
}
Compilation message (stderr)
boat.cpp: In function 'int main(int, char**)':
boat.cpp:39:17: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
scanf("%d", &N);
^
boat.cpp:41:34: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
scanf("%d%d", &(A[i]), &(B[i]));
^
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