Merge pull request #1389 from Jerry-306/patch-61

0494.目标和 新增typescript版本代码

problems/0494.目标和.md

@@ -351,22 +351,26 @@ const findTargetSumWays = (nums, target) => {
 };
 ```
 
-TypeScript：
 
-```typescript
+TypeScript:
+
+```ts
 function findTargetSumWays(nums: number[], target: number): number {
-    const sum: number = nums.reduce((pre, cur) => pre + cur);
-    if (Math.abs(target) > sum) return 0;
-    if ((target + sum) % 2 === 1) return 0;
-    const bagSize: number = (target + sum) / 2;
-    const dp: number[] = new Array(bagSize + 1).fill(0);
-    dp[0] = 1;
-    for (let i = 0; i < nums.length; i++) {
-        for (let j = bagSize; j >= nums[i]; j--) {
+    // 把数组分成两个组合left, right.left + right = sum, left - right = target.
+    const sum: number = nums.reduce((a: number, b: number): number => a + b);
+    if ((sum + target) % 2 || Math.abs(target) > sum)  return 0;
+    const left: number = (sum + target) / 2;
+    
+    // 将问题转化为装满容量为left的背包有多少种方法
+    // dp[i]表示装满容量为i的背包有多少种方法
+    const dp: number[] = new Array(left + 1).fill(0);
+    dp[0] = 1;  // 装满容量为0的背包有1种方法（什么也不装）
+    for (let i: number = 0; i < nums.length; i++) {
+        for (let j: number = left; j >= nums[i]; j--) {
             dp[j] += dp[j - nums[i]];
         }
     }
-    return dp[bagSize];
+    return dp[left];
 };
 ```