poj-1013

//684K  0MS G++
#include <cstdio>
#include <cstring>
#include <iostream>
#include <cstring>

using namespace std;

char coins[12];

// char weightingRes[3][30];
char weightingRes[30];

char leftPart[10];
char rightPart[10];
char res[10];

int weighttingInfo[3][20]; // 0: even 1: light

char lightWeighttingNum;

int weightSideNum;

void fillInfo(char * leftPart, char * rightPart, char * res) {
    // printf("%s\n", info);
    char flag = 0;
    // printf("%s %s %s\n", leftPart, rightPart, res);
    if (!strcmp("up", res)) {
        flag = 1;
        char inSideFlag[12] = {0};

        for (int i = 0; i < strlen(leftPart); i++) {
            if (coins[leftPart[i] - 'A'] != 3) {
                if (coins[leftPart[i] - 'A'] == -flag) {
                    coins[leftPart[i] - 'A'] = 3;
                } else {
                    coins[leftPart[i] - 'A'] = flag;
                }
            }
            
            inSideFlag[leftPart[i] - 'A'] = 1;
        }

        flag = -1;

        for (int i = 0; i < strlen(rightPart); i++) {
            if (coins[rightPart[i] - 'A'] != 3) {
                if (coins[rightPart[i] - 'A'] == -flag) {
                    coins[rightPart[i] - 'A'] = 3;
                } else {
                    coins[rightPart[i] - 'A'] = flag;
                }
            }
            
            inSideFlag[rightPart[i] - 'A'] = 1;
        }

        for (int i = 0; i < 12; i++) {
            if (!inSideFlag[i]) {
                coins[i] = 3;
            }
        }
    } else if (!strcmp("down", res)) {
        flag = -1;
        char inSideFlag[12] = {0};

        for (int i = 0; i < strlen(leftPart); i++) {
            if (coins[leftPart[i] - 'A'] != 3) {
                if (coins[leftPart[i] - 'A'] == -flag) {
                    coins[leftPart[i] - 'A'] = 3;
                } else {
                    coins[leftPart[i] - 'A'] = flag;
                }
            }
            
            inSideFlag[leftPart[i] - 'A'] = 1;
        }

        flag = 1;

        for (int i = 0; i < strlen(rightPart); i++) {
            if (coins[rightPart[i] - 'A'] != 3) {
                if (coins[rightPart[i] - 'A'] == -flag) {
                    coins[rightPart[i] - 'A'] = 3;
                } else {
                    coins[rightPart[i] - 'A'] = flag;
                }
            }
            
            inSideFlag[rightPart[i] - 'A'] = 1;
        }

        for (int i = 0; i < 12; i++) {
            if (!inSideFlag[i]) {
                coins[i] = 3;
            }
        }
    } else {
        flag = 3;
        for (int i = 0; i < strlen(leftPart); i++) {
            coins[leftPart[i] - 'A'] = 3;
        }

        for (int i = 0; i < strlen(rightPart); i++) {
            coins[rightPart[i] - 'A'] = 3;
        }
    }
}

void solve() {
    // printf("solve\n");
    for (int i = 0; i < 12; i++) {
        
        if (coins[i] == -1) {
            printf("%c is the counterfeit coin and it is light. \n", i+'A');
            return;
        } else if (coins[i] == 1) {
            printf("%c is the counterfeit coin and it is heavy. \n", i+'A');
            return;
        }
    }
}

int caseNum;
int main() {
    scanf("%d\n", &caseNum);
    for (int i = 1; i <= caseNum; i++) {
        memset(weighttingInfo, 0, sizeof(weighttingInfo));
        memset(coins, 0, sizeof(coins));
        lightWeighttingNum = 0;
        for (int i = 0; i <= 2; i++) {
            // fgets(weightingRes, sizeof(weightingRes), stdin);
            scanf("%s%s%s", leftPart, rightPart, res);
            fillInfo(leftPart, rightPart, res);
        }
        solve();
    }
}

http://blog.youkuaiyun.com/lyy289065406/article/details/6661421

不看网上的discuss我还真想不出这个思路：
1) 平衡状态，所有参与称重的硬币都是真的；
2) 非平衡状态，所有没有参与称重的硬币都是真的；
3) 若有一枚硬币既出现在重的一边，又出现在轻的一边，则这枚硬币是真的；

经过以上3重筛选，剩下的硬币恰好1枚，否则答案不唯一。

把上面的处理技巧记着吧，以后再有类似天平的题可以参考一下.