Polish the content

Polish the chapter preface, introduction and complexity anlysis

codes/cpp/chapter_computational_complexity/time_complexity.cpp

@@ -67,7 +67,7 @@ int bubbleSort(vector<int> &nums) {
 /* 指数阶（循环实现） */
 int exponential(int n) {
     int count = 0, base = 1;
-    // cell 每轮一分为二，形成数列 1, 2, 4, 8, ..., 2^(n-1)
+    // 细胞每轮一分为二，形成数列 1, 2, 4, 8, ..., 2^(n-1)
     for (int i = 0; i < n; i++) {
         for (int j = 0; j < base; j++) {
             count++;