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44 lines
911 B
44 lines
911 B
2 years ago
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package class10;
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// 测试链接 : https://leetcode.com/problems/k-inverse-pairs-array/
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public class Code03_KInversePairs {
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public static int kInversePairs(int n, int k) {
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if (n < 1 || k < 0) {
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return 0;
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}
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int[][] dp = new int[n + 1][k + 1];
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dp[0][0] = 1;
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int mod = 1000000007;
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for (int i = 1; i <= n; i++) {
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dp[i][0] = 1;
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for (int j = 1; j <= k; j++) {
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dp[i][j] = (dp[i][j - 1] + dp[i - 1][j]) % mod;
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if (j >= i) {
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dp[i][j] = (dp[i][j] - dp[i - 1][j - i] + mod) % mod;
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}
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}
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}
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return dp[n][k];
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}
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public static int kInversePairs2(int n, int k) {
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if (n < 1 || k < 0) {
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return 0;
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}
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int[][] dp = new int[n + 1][k + 1];
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dp[0][0] = 1;
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for (int i = 1; i <= n; i++) {
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dp[i][0] = 1;
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for (int j = 1; j <= k; j++) {
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dp[i][j] = dp[i - 1][j] + dp[i][j - 1];
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if (j >= i) {
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dp[i][j] -= dp[i - 1][j - i];
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}
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}
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}
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return dp[n][k];
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}
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}
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