Va 10317-equating equations greedy DFS

Va 10317-equating equations greedy DFS

ACM

Address: Ultraviolet A 10317-equating Equations

Question:
Give an equation, but this equation is not necessarily correct. You need to re-sort the numbers in the peering formula to make the equation true. The equation has only + and-, and the number of digits is less than 16.

Analysis:
Toa + b - c = d - eFor example.
1. We change all the items on the right of the equation to the left,a + b - c - d + e = 0 
2. Put the + item and-item together and it becomes(a + b + e) - (c + d) = 0 
3. Then(a + b + e) = (c + d) 
4. so the sum and sum of all numbers should be an even number. Then we only need to find the number of-items, DFS finds the same number, and sum/2, then the equation can be established.
5. The output is a manual problem.

Code:

/**  Author:      illuz <iilluzen[at]gmail.com>*  File:        10317.cpp*  Create Date: 2014-06-27 14:52:46*  Descripton:  brute force */#include <cstdio>#include <cstring>#include <iostream>#include <algorithm>using namespace std;const int N = 100;bool pom[2][N];// plus or minus, 0 is plus, 1 is minusint lterm, rterm;char eqt[N];int sum, num[N], cnt, mcnt;bool choose[N];void init() {char tmp[4];int len = strlen(eqt), prev = 0, dpom = 0, npom = 0;cnt = 0;mcnt = 0;sum = 0;for (int i = 0; i < len; ) {sscanf(eqt + i, "%s", tmp);if (tmp[0] == '+') {pom[dpom][npom++] = 0;prev = 0;} else if (tmp[0] == '-') {pom[dpom][npom++] = 1;prev = 1;} else if (tmp[0] == '=') {dpom++;lterm = npom;npom = 0;prev = 0;} else {mcnt += dpom ^ prev;sscanf(tmp, "%d", &num[cnt]);sum += num[cnt];cnt++;}i += strlen(tmp) + 1;}rterm = npom;}bool dfs(int restsum, int pos, int restcnt) {if (restcnt == 0)return restsum == 0;if (restsum < 0 || restcnt < 0)return false;for (int i = pos; i <= cnt - restcnt; i++) {choose[i] = 1;if (dfs(restsum - num[i], i + 1, restcnt - 1))return true;choose[i] = 0;}return false;}bool solve() {memset(choose, 0, sizeof(choose));if (sum % 2) {return false;}return dfs(sum / 2, 0, mcnt);}void print() {int p[N], m[N], pcnt = 0, mcnt = 0;for (int i = 0; i < cnt; i++) {if (choose[i]) {m[mcnt++] = num[i];} else {p[pcnt++] = num[i];}// cout << choose[i] << ' ';}printf("%d", p[--pcnt]);for (int i = 0; i < lterm; i++) {if (pom[0][i] == 0) {printf(" + %d", p[--pcnt]);} else {printf(" - %d", m[--mcnt]);}}printf(" = %d", m[--mcnt]);for (int i = 0; i < rterm; i++) {if (pom[1][i] == 1) {printf(" - %d", p[--pcnt]);} else {printf(" + %d", m[--mcnt]);}}puts("");}int main() {while (gets(eqt)) {init();if (solve()) {print();} else {puts("no solution");}}return 0;}