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洛谷1873
核心感悟：
①：关于check()函数：一旦这种和计算总和有关的判断函数——sum=0一定要写在前面
②：由于二分查找的答案可能巨大，干脆全部用long long
判断的思想：
①：主轴：就是答案和范围的那条线，如锯片的高度，分的蛋糕的边长。
②：副轴：要求达到的那个变量。
#include<bits/stdc++.h> using namespace std; long long l=1,r=9e9; long long
sum=0;long long ans; long long n,k; bool check(long long arry[],long long m) {
sum=0; for(int i=1;i<=n;i++) { if(m<arry[i]) { sum+=arry[i]-m; } }
if(sum>=k)return 1; return 0; } int main() { scanf("%lld%lld",&n,&k); long long
arry[n+1]; for(int i=1;i<=n;i++)scanf("%lld",&arry[i]); while(l<=r) { long long
m=l+(r-l)/2; if(check(arry,m)) { ans=m; l=m+1; } else r=m-1; }
printf("%lld",ans); return 0; }
洛谷2440
本人写错的地方：
while循环中的核心代码r=m+1和l=m-1出现了问题。（写反了）
忘记写while里面的代码段int m=l+(r-l)/2;（调试以后才发现的）
