ZOJ-2492

模拟解方程，有点小繁琐，逻辑处理的时候一定要细心，测试数据下载：http://sharif.ir/~acmicpc/acmicpc03/index.html

#include<stdio.h>
#include<string.h>
#include<math.h>

static int calc(int a, int b, char op, int right)
{
	if (!right)
		return op == '+' ? a + b : a - b;
	else
		return op == '+' ? a - b : a + b;
}

int main()
{
	int t;
	char s[256];
	scanf("%d", &t);
	while (getchar() != '\n')
		;
	while (t--)
	{
		gets(s);
		int right = 0, i, l = strlen(s), temp = 0, prev = 0, prevx = 0;
		char c, op = '+';
		for (i = 0; i < l; i++)
		{
			c = s[i];
			if (c == '+' || c == '-')
			{
				prev = calc(prev, temp, op, right);
				op = c;
				temp = 0;
			}
			else if (c >= '0' && c <= '9')
			{
				temp = temp * 10 + c - '0';
			}
			else if (c == 'x')
			{
				if (!temp)
					temp = 1;
				prevx = calc(prevx, temp, op, right);
				temp = 0;
			}
			else if (c == '=')
			{
				if (temp)
					prev = calc(prev, temp, op, right);
				right = 1;
				temp = 0;
				op = '+';
			}
		}
		if (temp)
			prev = calc(prev, temp, op, right);
		if (!prevx)
			puts(prev ? "IMPOSSIBLE" : "IDENTITY");
		else
			printf("%d\n", (int) floor(prev / (double) (-prevx)));
	}
	return 0;
}