Finding bipartite subgraphs efficiently

Polynomial algorithms are given for the following two problems: given a graph with $n$ vertices and $m$ edges, where $m \ge 3 n^{3/2}$, find a complete balanced bipartite subgraph with parts about $\ln n/(\ln (n^2/m))$, given a graph with $n$ vertices, find a decomposition of its edges into complete balanced bipartite graphs having altogether $O(n^2 / \ln n)$ vertices. Previous proofs of the existence of such objects, due to K\H{o}v\'ari-S\'os-Tur\'an, Chung-Erd\H{o}s-Spencer, Bublitz and Tuza were non-constructive.