Dynamic programming


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    M

    Jamie is walking along a number line that starts at point 0 and ends at point n. She can move either one step to the left or one step to the right of her current location , with the exception that she cannot move left from point 0 or right from point n. In other words, if Jamie is standing at point i,she can move to either i-1 or i+1 as long as her destination exists in the inclusive range [0,n]. She has a string ,s , of movement instruction consisting of the letters 1 and r , where 1 is an instruction to move one step left and r is an instruction to move one step right.
    Jamie followed the instructions in s one by one and in order .For Example if s=‘rrlr’,she performs the following sequence of moves :one step right ->one step right ->one step left -> one step right .Jamie wants to move from point x to point y following some subsequence of string s instruction and wonders how many distinct possible subsequence of string s will get her from point x to point y. recall that a subsequence of a string is obtained by deleting zero or more characters from string .

    it has four parameters
    A String , s giving a sequence of eduction using the characters l( i.e. move left one unit ) and r (i.e. move right one unit)
    An integer n, denoting the length of the number line.
    An integer x, denoting jamie’s starting point on the number line
    An integer y , denoting Jamie’s enidng point on the number line.
    The function must return an integer denoting the total number of distinct subsequence of string s that will lead Jamie from point x to point y as this value cab be quite large .

    Sample Input
    rrlrlr
    6
    1
    2

    out put =7


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