CodeForces 712C Memory and De-Evolution (贪心+暴力)

题意：现在有一个长度为 x 的正三角形，每次可以把一条边减小，然后用最少的时间变成长度为 y 的正三角形。

析：一开始，正着想，然后有一个问题，就是第一次减小多少才能最快呢？这个好像并不好确定，然后我就可以倒着想，从一个小三角形变成一个大三角，

那么边长长的越快越好了，剩下的就暴力了。

代码如下：

#pragma comment(linker, "/STACK:1024000000,1024000000")
#include <cstdio>
#include <string>
#include <cstdlib>
#include <cmath>
#include <iostream>
#include <cstring>
#include <set>
#include <queue>
#include <algorithm>
#include <vector>
#include <map>
#include <cctype>
#include <cmath>
#include <stack>
#define freopenr freopen("in.txt", "r", stdin)
#define freopenw freopen("out.txt", "w", stdout)
using namespace std;

typedef long long LL;
typedef pair<int, int> P;
const int INF = 0x3f3f3f3f;
const double inf = 0x3f3f3f3f3f3f;
const double PI = acos(-1.0);
const double eps = 1e-8;
const int maxn = 1e5 + 5;
const int mod = 1e9 + 7;
const int dr[] = {-1, 0, 1, 0};
const int dc[] = {0, 1, 0, -1};
const char *de[] = {"0000", "0001", "0010", "0011", "0100", "0101", "0110", "0111", "1000", "1001", "1010", "1011", "1100", "1101", "1110", "1111"};
int n, m;
const int mon[] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
const int monn[] = {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
inline int Min(int a, int b){ return a < b ? a : b; }
inline int Max(int a, int b){ return a > b ? a : b; }
inline LL Min(LL a, LL b){ return a < b ? a : b; }
inline LL Max(LL a, LL b){ return a > b ? a : b; }
inline bool is_in(int r, int c){
    return r >= 0 && r < n && c >= 0 && c < m;
}
int a[4];

int main(){
    while(scanf("%d %d", &n, &m) == 2){
        a[2] = a[1] = a[0] = m;
        int ans = 0;
        while(a[0] != n){
            a[0] = Min(n, a[1] + a[2] - 1);
            sort(a, a+3);
            ++ans;
        }
        printf("%d
", ans);
    }
    return 0;
}