newcoder F石头剪刀布（DFS + 思维）题解

#include<set>
#include<map>
#include<stack>
#include<cmath>
#include<queue>
#include<string>
#include<cstdio>
#include<cstring>
#include<sstream>
#include<iostream>
#include<algorithm>
typedef long long ll;
using namespace std;
const int maxn = (1 << 21) + 10;
const int MOD = 1e9 + 7;
const int INF = 0x3f3f3f3f;
int R, P, S, cnt;
int r, p, s;
char ans[maxn];
void dfs(char x, int L, int R){
    if(L == R){
        ans[L] = x;
        if(x == ‘R‘) r++;
        else if(x == ‘P‘) p++;
        else if(x == ‘S‘) s++;
        return;
    }
    int m = (L + R) >> 1;
    if(x == ‘R‘){
        dfs(‘R‘, L, m);
        dfs(‘S‘, m + 1, R);
    }
    else if(x == ‘P‘){
        dfs(‘P‘, L, m);
        dfs(‘R‘, m + 1, R);
    }
    else if(x == ‘S‘){
        dfs(‘S‘, L, m);
        dfs(‘P‘, m + 1, R);
    }
    bool swapp = false;
    for(int i = L; i <= m; i++){
        if(ans[i] < ans[m + i - L + 1]) break;
        if(ans[i] > ans[m + i - L + 1]){
            swapp = true;
            break;
        }
    }
    if(swapp){
        for(int i = L; i <= m; i++){
            swap(ans[i], ans[m + i - L + 1]);
        }
    }
}
int main(){
    scanf("%d%d%d", &R, &P, &S);  //r p s
    cnt = R + P + S;
    bool flag = false;
    for(int i = 0; i < 3; i++){
        r = p = s = 0;
        if(i == 0){
            dfs(‘R‘, 1, cnt);
        }
        else if(i == 1){
            dfs(‘P‘, 1, cnt);
        }
        else if(i == 2){
            dfs(‘S‘, 1, cnt);
        }
        if(R == r && P == p && S == s){
            flag = true;
            break;
        }
    }
    ans[cnt + 1] = ‘\0‘;
    if(flag) printf("%s\n", ans + 1);
    else printf("IMPOSSIBLE\n");
    return 0;
}