Weekly Contest 111-------->943. Find the Shortest Superstring(can't understand)
Given an array A of strings, find any smallest string that contains each string in A
as a substring.
We may assume that no string in A
is substring of another string in A
.
Example 1:
Input: ["alex","loves","leetcode"]
Output: "alexlovesleetcode"
Explanation: All permutations of "alex","loves","leetcode" would also be accepted.
Example 2:
Input: ["catg","ctaagt","gcta","ttca","atgcatc"]
Output: "gctaagttcatgcatc"
Note:
1 <= A.length <= 12
1 <= A[i].length <= 20
Approach #1:
class Solution {
public String shortestSuperstring(String[] A) {
int N = A.length; int [][] overlaps = new int[N][N];
for (int i = 0; i < N; ++i) {
for (int j = 0; j < N; ++j) {
int m = Math.min(A[i].length(), A[j].length());
for (int k = m; k >= 0; --k) {
if (A[i].endsWith(A[j].substring(0, k))) {
overlaps[i][j] = k;
break;
}
}
}
} int[][] dp = new int[1<<N][N];
int[][] parent = new int[1<<N][N];
for (int mask = 0; mask < (1<<N); ++mask) {
Arrays.fill(parent[mask], -1); for (int bit = 0; bit < N; ++bit) if (((mask >> bit) & 1) > 0) {
int pmask = mask ^ (1 << bit);
if (pmask == 0) continue;
for (int i = 0; i < N; ++i) if (((pmask >> i) & 1) > 0){
int val = dp[pmask][i] + overlaps[i][bit];
if (val > dp[mask][bit]) {
dp[mask][bit] = val;
parent[mask][bit] = i;
}
}
}
} int[] perm = new int[N];
boolean[] seen = new boolean[N];
int t = 0;
int mask = (1 << N) - 1; int p = 0;
for (int j = 0; j < N; ++j)
if (dp[(1 << N) - 1][j] > dp[(1 << N) - 1][p])
p = j; while (p != -1) {
perm[t++] = p;
seen[p] = true;
int p2 = parent[mask][p];
mask ^= 1 << p;
p = p2;
} for (int i = 0; i < t/2; ++i) {
int v = perm[i];
perm[i] = perm[t-1-i];
perm[t-1-i] = v;
} for (int i = 0; i < N; ++i) if (!seen[i])
perm[t++] = i; StringBuilder ans = new StringBuilder(A[perm[0]]);
for (int i = 1; i < N; ++i) {
int overlap = overlaps[perm[i-1]][perm[i]];
ans.append(A[perm[i]].substring(overlap));
} return ans.toString();
}
}
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