640.求解方程

rust/src/implements/mod.rs

@@ -136,6 +136,7 @@ mod q0623;
 mod q0628;
 mod q0633;
 mod q0636;
+mod q0640;
 mod q0643;
 mod q0674;
 mod q0684;

rust/src/implements/q0640.rs

@@ -0,0 +1,90 @@
+use std::fmt::format;
+use crate::Solution;
+
+impl Solution {
+    /// [640.求解方程](https://leetcode.cn/problems/solve-the-equation/)
+    ///
+    /// 2022-08-09 14:19:01
+    ///
+    /// 求解一个给定的方程，将`x`以字符串 `"x=#value"` 的形式返回。该方程仅包含 `'+'` ， `'-'` 操作，变量 `x` 和其对应系数。
+    ///
+    /// 如果方程没有解，请返回 `"No solution"` 。如果方程有无限解，则返回 `“Infinite solutions”` 。
+    ///
+    /// 如果方程中只有一个解，要保证返回值 'x' 是一个整数。
+    ///
+    /// + **示例 1：**
+    ///     + **输入:** equation = "x+5-3+x=6+x-2"
+    ///     + **输出:** "x=2"
+    /// + **示例 2:**
+    ///     + **输入:** equation = "x=x"
+    ///     + **输出:** "Infinite solutions"
+    /// + **示例 3:**
+    ///     + **输入:** equation = "2x=x"
+    ///     + **输出:** "x=0"
+    /// + **提示:**
+    ///     * `3 <= equation.length <= 1000`
+    ///     * `equation` 只有一个 `'='`.
+    ///     * `equation` 方程由整数组成，其绝对值在 `[0, 100]` 范围内，不含前导零和变量 `'x'` 。
+    /// + Related Topics
+    ///     * 数学
+    ///     * 字符串
+    ///     * 模拟
+    pub fn solve_equation(equation: String) -> String {
+        let (mut a,mut b,mut c) = (0, 0, 0);
+        let mut sign = 1;
+        let mut left = 1;
+        let mut has_c = false;
+        for z in equation.into_bytes() {
+            match z {
+                b'x' => {
+                    a += if has_c { sign * left * c } else { sign * left };
+                    c = 0;
+                    has_c = false;
+                }
+                b'+' => {
+                    b += sign * left * c;
+                    c = 0;
+                    sign = 1;
+                    has_c = false;
+                }
+                b'-' => {
+                    b += sign * left * c;
+                    c = 0;
+                    sign = -1;
+                    has_c = false;
+                }
+                b'=' => {
+                    b += sign * left * c;
+                    c = 0;
+                    sign = 1;
+                    left = -1;
+                    has_c = false;
+                }
+                _ => {
+                    c = c * 10 + (z - b'0') as i32;
+                    has_c = true;
+                }
+            }
+        }
+        b += sign * left * c;
+        match (a, b) {
+            (0, 0) => "Infinite solutions".to_owned(),
+            (0, _) => "No solution".to_owned(),
+            _ => format!("x={}", -b / a)
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use crate::Solution;
+
+    #[test]
+    fn test_q0640() {
+        assert_eq!(Solution::solve_equation("x+5-3+x=6+x-2".to_owned()), "x=2".to_owned());
+        assert_eq!(Solution::solve_equation("x=x".to_owned()), "Infinite solutions".to_owned());
+        assert_eq!(Solution::solve_equation("2x=x".to_owned()), "x=0".to_owned());
+        assert_eq!(Solution::solve_equation("0x=0".to_owned()), "Infinite solutions".to_owned());
+        assert_eq!(Solution::solve_equation("0=0x".to_owned()), "Infinite solutions".to_owned());
+    }
+}