feat: add solutions to lc problem: No.1920 (doocs#4032)

No.1920.Build Array from Permutation

Author: yanglbme

solution/1900-1999/1920.Build Array from Permutation/README.md

@@ -65,7 +65,11 @@ ans = [nums[nums[0]], nums[nums[1]], nums[nums[2]], nums[nums[3]], nums[nums[4]]
 
 <!-- solution:start -->
 
-### 方法一
+### 方法一：模拟
+
+我们可以直接模拟题目描述的过程，构建一个新的数组 $\textit{ans}$，对于每个 $i$，令 $\textit{ans}[i] = \textit{nums}[\textit{nums}[i]]$。
+
+时间复杂度 $O(n)$，其中 $n$ 是数组 $\textit{nums}$ 的长度。忽略答案数组的空间消耗，空间复杂度 $O(1)$。
 
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@@ -122,7 +126,7 @@ func buildArray(nums []int) []int {
 
 ```ts
 function buildArray(nums: number[]): number[] {
-    return nums.map(v => nums[v]);
+    return nums.map(x => nums[x]);
 }
 ```
 
@@ -144,11 +148,7 @@ impl Solution {
  * @return {number[]}
  */
 var buildArray = function (nums) {
-    let ans = [];
-    for (let i = 0; i < nums.length; ++i) {
-        ans[i] = nums[nums[i]];
-    }
-    return ans;
+    return nums.map(x => nums[x]);
 };
 ```
 

solution/1900-1999/1920.Build Array from Permutation/README_EN.md

@@ -29,7 +29,7 @@ tags:
 <pre>
 <strong>Input:</strong> nums = [0,2,1,5,3,4]
 <strong>Output:</strong> [0,1,2,4,5,3]<strong>
-Explanation:</strong> The array ans is built as follows: 
+Explanation:</strong> The array ans is built as follows:
 ans = [nums[nums[0]], nums[nums[1]], nums[nums[2]], nums[nums[3]], nums[nums[4]], nums[nums[5]]]
     = [nums[0], nums[2], nums[1], nums[5], nums[3], nums[4]]
     = [0,1,2,4,5,3]</pre>
@@ -62,7 +62,11 @@ ans = [nums[nums[0]], nums[nums[1]], nums[nums[2]], nums[nums[3]], nums[nums[4]]
 
 <!-- solution:start -->
 
-### Solution 1
+### Solution 1: Simulation
+
+We can directly simulate the process described in the problem by constructing a new array $\textit{ans}$. For each $i$, let $\textit{ans}[i] = \textit{nums}[\textit{nums}[i]]$.
+
+The time complexity is $O(n)$, where $n$ is the length of the array $\textit{nums}$. Ignoring the space consumption of the answer array, the space complexity is $O(1)$.
 
 <!-- tabs:start -->
 
@@ -119,7 +123,7 @@ func buildArray(nums []int) []int {
 
 ```ts
 function buildArray(nums: number[]): number[] {
-    return nums.map(v => nums[v]);
+    return nums.map(x => nums[x]);
 }
 ```
 
@@ -141,11 +145,7 @@ impl Solution {
  * @return {number[]}
  */
 var buildArray = function (nums) {
-    let ans = [];
-    for (let i = 0; i < nums.length; ++i) {
-        ans[i] = nums[nums[i]];
-    }
-    return ans;
+    return nums.map(x => nums[x]);
 };
 ```
 

solution/1900-1999/1920.Build Array from Permutation/Solution.js

@@ -3,9 +3,5 @@
  * @return {number[]}
  */
 var buildArray = function (nums) {
-    let ans = [];
-    for (let i = 0; i < nums.length; ++i) {
-        ans[i] = nums[nums[i]];
-    }
-    return ans;
+    return nums.map(x => nums[x]);
 };

solution/1900-1999/1920.Build Array from Permutation/Solution.ts

@@ -1,3 +1,3 @@
 function buildArray(nums: number[]): number[] {
-    return nums.map(v => nums[v]);
+    return nums.map(x => nums[x]);
 }

solution/1900-1999/1996.The Number of Weak Characters in the Game/README_EN.md

@@ -68,7 +68,15 @@ tags:
 
 <!-- solution:start -->
 
-### Solution 1
+### Solution 1: Sorting + Traversal
+
+We can sort all characters in descending order of attack power and ascending order of defense power.
+
+Then, traverse all characters. For the current character, if its defense power is less than the previous maximum defense power, it is a weak character, and we increment the answer by one. Otherwise, update the maximum defense power.
+
+After the traversal, we get the answer.
+
+The time complexity is $O(n \times \log n)$, and the space complexity is $O(\log n)$. Here, $n$ is the number of characters.
 
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