Plus longue sous-séquence commune

char *plssc(char *s, char *t) {
    int n = strlen(s), m = strlen(t);
    int **l = creer_matrice(n+1, m+1);

    /* Phase 1 — Initialisation */
    for (int i = 0; i <= n; i++) { l[i][0] = 0; }
    for (int j = 0; j <= m; j++) { l[0][j] = 0; }

    /* Phase 2 — Remplissage */
    for (int i = 1; i <= n; i++) {
        for (int j = 1; j <= m; j++) {
            if (s[i-1] == t[j-1]) {
                l[i][j] = 1 + l[i-1][j-1]; /* match → diagonale */
            } else {
                l[i][j] = max(l[i-1][j], l[i][j-1]); /* max voisins */
            }
        }
    }

    /* Phase 3 — Remontée */
    char *x = (char*)malloc(sizeof(char) * (l[n][m] + 1));
    x[l[n][m]] = '\0';
    int i = n, j = m, k = l[n][m] - 1;
    while (k >= 0) {
        if      (l[i][j] == l[i-1][j]) { i--; }
        else if (l[i][j] == l[i][j-1]) { j--; }
        else { x[k] = s[i-1]; i--; j--; k--; }
    }

    detruire_matrice(l, n+1, m+1);
    return x;
}