@@ -19,24 +19,15 @@ public class Code_0024_NowCoder_SmallSum {
1919 private static final int [] arr = new int [MAXN ];
2020 private static final int [] help = new int [MAXN ];
2121 private static int n ;
22- 23- public static void main (String [] args ) throws IOException {
24- try (BufferedReader br = new BufferedReader (new InputStreamReader (System .in ))) {
25- StreamTokenizer in = new StreamTokenizer (br );
26- try (PrintWriter out = new PrintWriter (new OutputStreamWriter (System .out ))) {
27- in .nextToken ();
28- n = (int ) in .nval ;
29- for (int i = 0 ; i < n ; i ++) {
30- in .nextToken ();
31- arr [i ] = (int ) in .nval ;
32- }
33- out .println (smallSum (0 , n - 1 ));
34- out .flush ();
35- }
22+ public static void main (String [] args ) {
23+ Scanner in = new Scanner (System .in );
24+ n = in .nextInt ();
25+ for (int i = 0 ; i < n ; i ++) {
26+ arr [i ] = in .nextInt ();
3627 }
28+ System .out .println (smallSum (0 , n - 1 ));
3729 }
38- 39- // 结果比较大,用int会溢出的,所以返回long类型
30+ // 结果比较大,用int会溢出的,所以返回long类型
4031 // 时间复杂度O(n * logn)
4132 public static long smallSum (int l , int r ) {
4233 if (l == r ) {
@@ -49,22 +40,22 @@ public static long smallSum(int l, int r) {
4940 // 返回跨左右产生的小和累加和,左侧有序、右侧有序,让左右两侧整体有序
5041 public static long merge (int l , int m , int r ) {
5142 long ans = 0L ;
52- int i = l ; // 卡左边界
53- int j = m + 1 ; // 卡右边界
5443 long sum = 0L ;
55- while (j <= r ) {
56- // 滑动窗口,不回退
57- while (i <= m && arr [i ] <= arr [j ]) {
58- sum += arr [i ++];
59- }
60- ans += sum ;
61- j ++;
62- }
6344 int s = l ;
6445 int e = m + 1 ;
65- i = l ;
46+ while (e <= r ) {
47+ while (s <= m && arr [s ] <= arr [e ]) {
48+ ans += arr [s ++];
49+ }
50+ sum += ans ;
51+ e ++;
52+ }
53+ // help = new int[r - l + 1];
54+ s = l ;
55+ e = m + 1 ;
56+ int i = 0 ;
6657 while (s <= m && e <= r ) {
67- if (arr [s ] <= arr [e ]) {
58+ if (arr [s ] < arr [e ]) {
6859 help [i ++] = arr [s ++];
6960 } else {
7061 help [i ++] = arr [e ++];
@@ -76,9 +67,10 @@ public static long merge(int l, int m, int r) {
7667 while (e <= r ) {
7768 help [i ++] = arr [e ++];
7869 }
70+ int index = 0 ;
7971 for (i = l ; i <= r ; i ++) {
80- arr [i ] = help [i ];
72+ arr [i ] = help [index ++ ];
8173 }
82- return ans ;
74+ return sum ;
8375 }
8476}
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