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903.java
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903.java
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__________________________________________________________________________________________________
sample 2 ms submission
class Solution {
private int mod = (int)(1e9+7);
public int numPermsDISequence(String S) {
int n = S.length();
int[][] dp = new int[n+1][n+1];
for (int j=0; j<=n; j++) {
dp[0][j] = 1;
}
for (int i=1; i<=n; i++) {
char c = S.charAt(i-1);
int count = 0;
if (c == 'I') {
for (int j=0; j<=n-i; j++) {
count += dp[i-1][j];
count %= mod;
dp[i][j] = count;
}
} else {
for (int j=n-i; j>=0; j--) {
count += dp[i-1][j+1];
count %= mod;
dp[i][j] = count;
}
}
}
return dp[n][0];
// TLE
/*
int count = 0, n = S.length() + 1;
boolean[] visited = new boolean[n];
for (int i=0; i<n; i++) {
count += helper(i, 0, visited, S);
count %= mod;
}
return count;
*/
}
private int helper(int num, int i, boolean[] visited, String S) {
if (i == S.length()) {
return 1;
}
visited[num] = true;
int count = 0, n = visited.length;
char c = S.charAt(i);
if (c == 'D') {
for (int j=num-1; j>=0; j--) {
if (visited[j]) {
continue;
}
count += helper(j, i+1, visited, S);
count %= mod;
}
} else {
for (int j=num+1; j<n; j++) {
if (visited[j]) {
continue;
}
count += helper(j, i+1, visited, S);
count %= mod;
}
}
visited[num] = false;
return count;
}
}
__________________________________________________________________________________________________
sample 37064 kb submission
class Solution {
public int numPermsDISequence(String S) {
int n = S.length(), mod = (int)1e9 + 7;
int[][] dp = new int[n + 1][n + 1];
for (int j = 0; j <= n; j++) dp[0][j] = 1;
for (int i = 0; i < n; i++)
if (S.charAt(i) == 'I')
for (int j = 0, cur = 0; j < n - i; j++)
dp[i + 1][j] = cur = (cur + dp[i][j]) % mod;
else
for (int j = n - i - 1, cur = 0; j >= 0; j--)
dp[i + 1][j] = cur = (cur + dp[i][j + 1]) % mod;
return dp[n][0];
}
}
__________________________________________________________________________________________________