题解 | 小红的矩阵

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        long a=in.nextLong();
        long b=in.nextLong();
        long c=in.nextLong();
        System.out.println(findKthNumber(a,b,c));
    }
    private static long findKthNumber(long a,long b,long c){
        long left=1;
        long right=a*b;
        while(left<right){
            long mid=left+(right-left)/2;
            if(countLessOrEqual(mid,a,b)>=c){
                right=mid;
            }else{
                left=mid+1;
            }
        }
        return left;
    }
    private static long countLessOrEqual(long x,long a,long b){
        long count=0;
        for(long i=1;i<=a;i++){
            count+=Math.min(x/i,b);
            if(count>=Long.MAX_VALUE){
            break;
        }
    }
    return count;
}
}