Remove Element

Q:

Given an array and a value, remove all instances of that value in place and return the new length.

The order of elements can be changed. It doesn't matter what you leave beyond the new length.

A：

 

找到左边第一个等于elem的值，找到右边第一个不等于elem的值，两者互换，搞定

class Solution {
public:
    int removeElement(int A[], int n, int elem) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int l = 0;
        int r = n - 1;
        while (l <= r) {
            while (A[l] != elem && l <= n - 1) {
                ++l;
            }
            while (A[r] == elem && l >= 0) {
                --r;
            }
            if (l < r && l <= n - 1 && r >= 0) {
                swap(A[l], A[r]);
            }
        }
        return l;
    }
};