CF Codeforces Round #256 (Div. 2) D (448D) Multiplication Table，

CF Codeforces Round #256 (Div. 2) D (448D) Multiplication Table，

二分！！！

AC代碼如下：

#include<iostream>#include<cstring>#include<cstdio>#define ll long longusing namespace std;ll n,m,k;ll work(ll a){    ll i,j;    ll ans=0;    for(i=1;i<=n;i++)    {        j=a/i;        if(j>m)            j=m;        ans+=j;    }    return ans;}int main(){    scanf("%I64d%I64d%I64d",&n,&m,&k);    ll l,r,mid;    l=1;    r=n*m+1;    while(l<r)    {        mid=(l+r)/2;        //cout<<mid<<"!!!!!!!!!!!!!!!!!!!!!!"<<work(mid)<<endl;        if(work(mid)<k) l=mid+1;        else r=mid;    }    cout<<r<<endl;    return 0;}