CSES Coin comb I TLE: why?

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Автор bobbilyking, история, 6 лет назад, По-английски

i did look at the CF editorial, and yeah my implementation (i don't think) is wrong. and someone else had the same TLE problem as me but he never said how he resolved it (if he ever did). Is this just a java thing? Editorial says that time complexity is n * target, which is 10^8 operations, so maybe I can make very very slight optimizations somewhere to get it under 1ms?

bobbilyking
6 лет назад
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Bekh

6 лет назад, скрыть # |

I also got TLE with recursive dp in c++ and had to do iterative. Timelimit is strict but 10^8 is indeed the intended complexity. Try swapping out the modding line with this as mod is a heavy operation.

if (whatever >= MOD) whatever -= MOD

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bobbilyking

6 лет назад, скрыть # ^ |

omg that worked ty

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thedagger

6 лет назад, скрыть # ^ |

Had been scratching my head around what further to optimize....well there's always an optimization ty :)

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anushh23

5 лет назад, скрыть # ^ |

woahhh, it really worked!! But I found another code online and it makes the use of MOD but it didn't get any TLE, how is that possible. LINK: https://usaco.guide/problems/cses-1635-coin-combinations-i-unordered/solution

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Bekh

5 лет назад, скрыть # ^ |

I don't remember if that optimization was required in C++ codes for this problem or not. If it was, I have no idea tbh.

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pajenegod

5 лет назад, скрыть # ^ |

Btw one thing to note about this problem. You don't even need $$$n \cdot x$$$ mod calls.

Here is the solution with n * x mod calls

vector<ll> dp(x + 1);
dp[0] = 1;
for (int weight = 1; weight <= x; weight++) {
	for (int i = 0; i < n; i++) {
		if(weight - coins[i] >= 0) {
			dp[weight] += dp[weight - coins[i]];
			dp[weight] %= MOD;
		}
	}
}

Here is the solution with x mod calls

vector<ll> dp(x + 1);
dp[0] = 1;
for (int weight = 1; weight <= x; weight++) {
	for (int i = 0; i < n; i++) {
		if(weight - coins[i] >= 0) {
			dp[weight] += dp[weight - coins[i]];
		}
	}
        dp[weight] %= MOD;
}

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anushh23

5 лет назад, скрыть # ^ |

Thanks

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iamparthabhowmik

4 года назад, скрыть # ^ |

It works, thanks.

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CodeSlayer007

5 лет назад, скрыть # |

← Rev. 2 →

Not sure in java but in C++ a%b works slightly faster if b is a constant. So in the following code int mod = 1e9 + 7 will give TLE but int const mod = 1e9 + 7 will not.

dp[0] = 1;
    for (int i = 1; i <= m; i++)
    {   for (int j = 1; j<= n; j++)
        {   int x = i - a[j];
            if (x >= 0)
                dp[i] = (dp[i] + dp[x])%mod;
        }
    }
    cout << dp[m];

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