Add 640 solution

Author: lidongjies

src/solution/mod.rs

@@ -8,6 +8,7 @@ mod s0136_single_number;
 mod s0622_design_circular_queue;
 mod s0623_add_one_row_to_tree;
 mod s0636_exclusive_time_of_function;
+mod s0640_solve_the_equation;
 mod s0761_special_binary_string;
 mod s0899_orderly_queue;
 mod s1374_generate_a_string_with_characters_that_have_odd_counts;

src/solution/s0640_solve_the_equation.rs

@@ -0,0 +1,74 @@
+use std::num;
+
+/**
+ * [640] solve the equation
+ * https://leetcode.cn/problems/solve-the-equation/
+ */
+
+pub struct Solution {}
+
+impl Solution {
+    pub fn solve_equation(equation: String) -> String {
+        let mut factor = 0;
+        let mut value = 0;
+        let mut sign1 = 1_i32;
+        let mut index = 0;
+        let len = equation.len();
+        let chars: Vec<char> = equation.chars().collect();
+
+        while index < len {
+            // 判断是否为等号，更改默认系数
+            if chars[index] == '=' {
+                sign1 = -1;
+                index += 1;
+                continue;
+            }
+
+            let mut sign2 = sign1;
+            let mut number = 0_i32;
+            let mut valid = false;
+            // 判断是否为正负号，设置当前项的系数
+            if chars[index] == '-' || chars[index] == '+' {
+                sign2 = if chars[index] == '-' { -sign1 } else { sign1 };
+                index += 1;
+            }
+
+            // 判断是否为合法数字，并进行累加
+            while index < len && chars[index].is_digit(10) {
+                number = number * 10 + chars[index].to_digit(10).unwrap() as i32;
+                index += 1;
+                valid = true;
+            }
+
+            // 判断是否为变量x，并设置对 factor 累加
+            if index < len && chars[index] == 'x' {
+                factor += if valid { number * sign2 } else { sign2 };
+                index += 1;
+            } else {
+                value += sign2 * number;
+            }
+        }
+        if factor == 0 {
+            if value == 0 {
+                "Infinite solutions".to_string()
+            } else {
+                "No solution".to_string()
+            }
+        } else {
+            format!("x={:}", (-value / factor))
+        }
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_640() {
+        assert_eq!(
+            Solution::solve_equation("x+5-3+x=6+x-2".to_string()),
+            "x=2".to_string()
+        )
+    }
+}