百度之星初赛（1） 1003 序列变换 二分搜索

#include <cstdio>
#include <iostream>
#include <cstring>
#include <set>
#include <cmath>
#include <algorithm>
#include <vector>
#include <map>

using namespace std;

int n;
int a[100015];
int b[100015];

int fun(int m){
    for(int i = 0;i < n;i++){
        if(i == 0){
            b[i] = a[i]-m;
        }
        else{
            if(a[i]+m < b[i-1]+1){
                return 0;
            }
            else{
                if(a[i]-m < b[i-1]+1){
                    b[i] = b[i-1] + 1;
                }
                else
                {
                    b[i] = a[i] - m;
                }
            }
        }
    }
    return 1;
}
int main(){

    int t;
    cin >> t;
    for(int kcase = 1; kcase <= t;kcase ++){
        scanf("%d",&n);
        int maxn = 0;
        for(int i = 0;i < n;i++){
            scanf("%d",&a[i]);
            if(a[i] > maxn){
                maxn = a[i];
            }
        }        

        int l = 0;
        int r = 1000000+1;
        memset(b,0,sizeof(b));
        while(l < r){
            int m = l + (r-l)/2;
            if(fun(m)){
                r = m;
            }
            else{
                l = m + 1;
            }
        }
        printf("Case #%d:\n",kcase);
        printf("%d\n",l);
    }
    return 0;
}