ESIEE - Unité IN3S02

Unité IN3S02 - TD3
Corrigé 2.1- Tableau inverse (*)

public static void inverse(int[] t) {
        int x ;
        int j ;
        for(int i = 0 ; i < (t.length)/2 ; i++ ) {
            j = t.length - i - 1 ;
            x    = t[i];
            t[i] = t[j];
            t[j] = x ;
        }
    }

2.2- Plus proche élément (*)

    /** PLus proche élément - Solution 1 */
    // (The reference is the index of the nearest element)
    public static double nearestElement1(double[] t, double x) {
        int indexNearest = 0;   // the reference
        double nearestDistance = Math.abs(t[0] - x) ;
        double currentDistance ;
        for (int i = 1 ; i < t.length ; i++ ) {
            currentDistance = Math.abs(t[i] - x) ;
            if (currentDistance < nearestDistance) {
                indexNearest = i ;
                nearestDistance = currentDistance ;
            }
        }
        return t[indexNearest] ;
    }

    /** Plus proche élément - Solution 2 */
    // (The reference is the value of the nearest element)
    public static double nearestElement2(double[] t, double x) {
        double nearestElement = t[0]; // the reference
        double nearestDistance = Math.abs(nearestElement - x);
        double currentDistance ;
        for (int i = 1 ; i < t.length ; i++ ) {
            currentDistance = Math.abs(t[i] - x) ;
            if (currentDistance < nearestDistance) {
                nearestElement = t[i] ;
                nearestDistance = currentDistance ;
            }
        }
        return nearestElement ;
    }

2.3- Palindrome (*)

/**
* @param   String s : characters not in ['a', 'z'] are
*          interpreted as non letters and are ignored
*/
public static boolean isPalindrome(String s) {
    char[] t = s.toCharArray() ;
    boolean ok = true ;
    int iLeft   = 0 ;
    int iMiddle = t.length / 2 ;
    int iRight = t.length - 1 ;
    do {
        if ('a'<=t[iLeft] && t[iLeft]<='z') {
            if ('a'<=t[iRight] && t[iRight]<='z') {
                ok = t[iLeft]==t[iRight] ;
                iLeft++;
                iRight--;
            } else {
                iRight--;
            }
        } else {
            iLeft++;
        }
} while (ok && iLeft<iMiddle && iMiddle<iRight);
    return ok ;
}

2.4- Horner (*)

public static double evalPolynom(double[] p, double x) {
    double value = 0 ;
    for(int i = p.length - 1 ; i >= 0 ; i--) {
        value = value*x + p[i] ;
    }
    return value ;
}

2.5- Eratosthène (*)

/**
* @param   n : natural integer
*/
public static boolean[] Eratosthen(int n) {
    boolean[] t = new boolean[n];
    int i ;
    // init
    t[0] = false ;
    for(i = 1 ; i < n ; i++ ) t[i] = true ;
    // Euclid's algorithm
    for(i = 2 ; i < n/2 ; i++ ) {
        if (t[i]) {
            for(int k = 2 ; i*k < n ; k++ ) {
                t[i*k] = false ;
            }
        }
    }
    return t;
}

2.6- Matrice symétrique (*)

public static boolean isSymetric(int[][] t) {
    boolean ok = true ;
    for(int i = 0 ; i < t.length && ok ; i++ )
    for(int j = 0 ; j < t[0].length && ok ; j++)
        ok = t[i][j]==t[j][i] ;
    return ok ;
}

2.7- Tri à bulles (**)

public static void bubbleSort(double[] t) {
    double x ;
    int i, j ;
    for(i = 0; i < t.length ; i++) {
        for(j = t.length-1 ; j > i ; j--) {
            if (t[j] < t[j-1]) {
                x = t[j] ;
                t[j] = t[j-1] ;
                t[j-1] = x ;
            }
        }
    }
}

2.8- Conversion tableau vers entier (**)

public static int toInt(char[] t) {
    boolean isNegative = t[0]=='-' ;
    int result = 0 ;
    int i = 0 ;
    if (t[0]=='+' || t[0]=='-') i = 1 ;
    for( ; i<t.length; i++) {
        result = result * 10 + (int)t[i] - (int)'0' ;
    }
    if (isNegative) result = -result ;
    return result ;
}